84SE: Common Causes for Blowing "Engine" Fuse in Block?
 

Note: 1985 GSL-SE, fuel injected...

Drove 30mi to work today and pulling into the parking lot, engine shuts off. Coasted to a safe spot and started troubleshooting;
1) Fusible Links - swapped at the shock tower, brown for black, no change. Swapped back.
2) Fuse Block - 20A fuse for Engine on IG1 circuit blown. Figuring this is just a bad fuse, throw a spare 20A fuse in, key turned to ON (*NOT start, no crank), fuse blows. Replace with 30A fuse, turn key to ON, START, engine fires briefly, fuse blows again.

Diagnostics;
A) Pulled all extraneous fuses in case there's a short. Put in another 20A fuse for Engine, turn key to ON, engine starts briefly, fuse blows.
B) Disconnected Alternator + and - terminals. Put in another 20A fuse for Engine, turn key to ON, fuse blows. Reconnected Alternator.
C) Disconnected Fuel Pump under the bin. Put in another 20A fuse for Engine, turn key to ON, fuse blows. Reconnected Fuel Pump connector.

What am I missing? Car has 238k mi, been a daily driver for decades and I've not encountered this before. Nothing else changed, no recent electrical work, no recent mechanical work, didnt even add fuel recently. Stumped for the moment and headed over to Foxed.ca to look at the wiring diagram...

Thanks for any assistance offered, and I can answer any questions you guys might have,

bad engine ground ....i always hav 2...add one it won't hurt

I have a monster ground going from the Battery (-) to the Alternator bracket. Been there for years. I'll recheck tightness, though.

look at your injector harness,follow engine harness back to firewall. Look for chafing,rubbing. Pull up pass side carpet and put eyes on all wiring to ecu,disconnect ecu. Put all fuses back in,turn key on,see if fuse blows,still blows? Leave ecu disconnected. Remove EGI fuse,substitute fuse for a test light,use some ground down 1/4"spade terminals to insert in place of fuse then jumper wires so you can attach light to them and move it to where you can see it as you're trying to determine short location(s).
Turn key on,if short is present light will be lit and will remain lit til short is located and resolved. If it's not lit,plug ECU in,if it lights,likely a driver shorted in ECU.No change? Pull fuel pump relay... while watching test light, tap on ECU and orient in different positions while doing so.
Still watching test light,wiggle,manipulate all wires from ecu up til where passes thru firewall. Give a good tug there. Same same underhood,start at battery,follow harness to engine and work all wires,connectors all the way back to firewall,then inside where harness comes thru to inside up to fusebox and to steering column. Test light blinking or going out and back on lets you know you're close to problem-within inches.

This is where i'd start and is quickest way to isolate or find source of problem. Next step is consulting wire diagram and disconnecting components fed from this circuit til problem found.
After all these(reliable)miles my money's on chafed/rubbed thru harness,ECU,or some component on that circuit pulling excessive current-in that order.
Post back what you find. Happy hunting.

Thank you, man - I appreciate it.
 

Will get some time tomorrow night to setup my test light and start digging into it.

These were my thoughts exactly. +1 for worn harness somewhere.

following for the fix, as stated check wiring, check wires at fuel pump too, i believe that its on that circuit too,maybe something got up there from the road and knocked a wire loose.

I unplugged the Fuel Pump inside the bin, so it's not a short at the pump or underneath, but I'll take a close look this weekend. Thanks again, guys.

Alright - spent some time troubleshooting this past weekend and last night, and here's what I've found (*haven't fixed it...);

Observations on Symptoms - not NEW symptoms, just things I've noticed since looking into the problem deeper;
* Tachometer wasn't registering for about the last month - coincides with cold weather when the tachometer usually sticks at startup but spins up correctly once the car interior gets warm. Recognizing that the Tach is driven by the Trailing Coil signal and is used for Fuel Injection Timing, points me toward a bad Trailing Ignitor (possibly) or Trailing Coil (unlikely).
* Pre-start Idiot Lights not lighting - AFTER this problem started, I've noticed that the idiot lights on the bottom row of dash panel don't light except for "Seatbelt" and "Brake" (e-brake). Normally, with key in ON position - not start - all idiot lights would be lit. Once started, they all should go out. Don't know if that's related, but after blowing the Engine fuse, a bunch of those lights no longer come on as expected...

Troubleshooting Steps Taken;
1) Shorted Wiring Harness? Built the test light rig to replace the fuse (thanks GSLSEforme) - plugged into the Engine fuse location which keeps blowing fuses, and with Key in Run (*not Start), the light comes on (ECU is plugged in). Then, starting at the Battery / Coils began moving the wiring harnesses around, all the way from injectors to the firewall in the engine bay, across the passenger side engine bay to the firewall, and then under the dash on both sides all the way to the ECU. At no point did the light even flicker. Pulled the carpet back on both sides, removed passenger kick panel and all ECU wiring intact / undamaged. Swapped the wide ECU connectors (2) for a backup N304 computer, and no change in the light. Replaced 20A fuse for the test rig, and when Key turned to Run (not Start), fuse pops. No change at all. Returned ECU plugs to original N304 ECU.

2) Shorted Fuel Pump? Installed SE-EGI Fuel Pump Shunt at Air Flow Meter connector. Unplugged Fuel Pump connector under driver's bin and installed Voltmeter, turned Key to Run and checked for 12v at Fuel Pump connector - no current. Plugged Fuel Pump back in. Obviously, no Fuel Pump operation, as no current is getting to it, so I started looking at...

3) Air Flow Meter (AFM) Shorted? Removed wide connector from AFM and plugged into spare AFM. Test Light never went out. Key to Run, and no Fuel Pump heard (shunt is still installed). Pushed open AFM door to turn on Fuel Pump switch - no change. Installed 20A fuse in fuse block instead of Test Light, turned Key to Run = blown fuse. Plugged original AFM back in. Dead end?

4) Alternator Shorted? Unplugged Alternator Voltage Regulator Plug and unscrewed Positive Terminal lead. Connected both to backup Alternator. No change in Test Light Rig (steady on), and installed 20A fuse in fuse block, turned Key to Run = blown fuse. Reconnected cable and connector to original Alternator.

Other possibilities (in order of likelihood);
A) Unplug ECU and install Test Light Rig in blown fuse position and recheck all wiring harnesses again. Maybe I misunderstood unplugging the ECU before doing this test...?
B) Replace Trailing Ignitor (*I have spares)?
C) Test Fuel Pump Relay for short? I couldn't find it under the dash... is it in the engine bay?
D) Main Engine Relay(s) shorted?
E) Check Relay under dash shorted? Possibly related to the idiot lights not working?
F) Fuel Pump wiring & ground? Unlikely, but getting stumped sucks!

Any tips or notes on my troubleshooting is always appreciated. Thanks for the help so far,

Made a little progress tonight; I unplugged the ECU and did the wiggling of the wiring harnesses with the Test Light plugged into the Engine fuse location, no change. While plugging the ECU back in, I *unplugged* the connector next to it, shown in the pics below, and this made the Test Light go from a bright 12v glow to a dim glow - hopefully indicating the short (less current / voltage due to short?). Here's the connector at the ECU under the passenger side foot panel;

http://oi65.tinypic.com/2qsbig2.jpg
Closer view of the connector showing count & wire colors:
http://oi67.tinypic.com/2db8mly.jpg

I'm not sure where that leaves me, and I'm hoping someone knows what this connector powers. Is my short circuit ON the components for this connector, or somewhere else? Also, now - with this connector UNPLUGGED - the dashboard idiot lights are lit correctly for Key in Run position (*all lit, prior to start). Thanks again,

It's either a short in the CPU or one in that part of the wiring harness and connecting it to the CPU completes that circuit. Hard to tell if the source of the voltage is coming from the CPU or the CPU completes the ground. What I would do is make a pinout and document the voltage of each pin with the connector unplugged. Next would be to plug it in and do the same check by back-probing the connectors. I don't like this part of it because the fuse will not be protecting the CPU at this point. I'll do some digging in the wiring diagram and see what this connector is and what the values are suppose to be.

By "CPU" ^^^, you mean "ECU = Emissions Control Unit" located under the passenger footwell, right?

I also studied the Wiring Diagram tonight, and this connector is called the "F - E" Connector, and connects the Front Wiring Harness to the Engine Wiring Harness. the Front Wiring Harness runs up the Indoor Fan Blower Motor, along the top front of the dashboard, over the center Air Vents and then to the Steering Column area where it splits off to the Combination Switch and other stuff under the driver's left foot.

As additional troubleshooting - under the belief that it's not a wiring harness short, but a bad component somewhere along this circuit;
1) Unplugged the Cruise Control Unit (B-03) - no change in Test Light, so plugged it back in.
2) Unplugged the Circuit Openning Relay (X-07, aka Fuel Pump Relay for EFI) - no change in Test Light, so plugged it back in.
3) Unplugged the Pressure Sensor (B-14, aka Altitude Compensator) - no change in Test Light, so plugged it back in.

Followed the wiring harness back to the driver's strut tower, and started checking connectors;
A) When unplugging the Vent / Vacuum Valve Relays (the two round relays attached nearest to the strut tower) - the Test Light went dim when I unplugged the front one. As I unplugged it, I could hear the relay click off, and the Test Light bulb got significantly dimmer than before. Plugged back in, the Test Light gets brighter.
B) Same as above when unplugging one of the connectors under the heavy rubber boot right next to it, as it gets/sends signal to/from the Vent / Vacuum Relays and the ECU.

Does any of this indicate a problem with either the V/V Relays? I don't have spares, but I do have spare Vent / Vacuum Solenoids. Thanks again for reading... this is really frustrating, and I miss driving my car!

More troubleshooting today...
 

Still unable to get the Test Light to go out, but found that unplugging the Alternator plug just below the RE-EGI air Box drops the intensity of the light bulb considerably to barely a glow. To recap, unplugging the Harness connector shown above drops the Test Light from BRIGHT to dim, then unplugging the Alternator connector which includes a black block bolted to the front corner of the RE-EGI air Box, and having the Positive lead which then connects to the Positive on the Alternator, drops the intensity of the Test Light to barely glowing.

Does this indicate a bad Alternator? Still troubleshooting,...

It would be easy enough to just take the alt to your favorite parts store for free testing. This might sound silly, but try adding an additional ground running from the big alt bolt to the shock tower or battery.

Are you doing this test with each successive component you unplug left disconnected or plugged back in as before?
Regarding possible damage to ecu,small test lamp bulb about 3 watts and filament in bulb can't pass enough current to damage anything.

Regarding alternator,did it charge properly previously to current complaint,did all warning lights at base of dash cluster go out completely especially the battery light when engine started and running? If so,not likely alternator is culprit here. Is alternator original? Are you disconnecting the output wire of alternator and the field plug. Try disconnecting field plug 1st and see what happens.
For a quick test take out test light jumpers and with everything still disconnected,put a rated fuse in and turn key on. If it does not blow,start connecting one component at a time and checking fuse as each is connected,leaving alternator field plug for last. Wherever the fuse blows,go back to last plugged in component and remove it and start checking that components' circuit. If all components that are connected don't blow fuse but it does blow when alternator connected,disconnect field plug,put in a new fuse and start car and let run for a few minutes.Plug in field connector,if car shuts off,fuse is blown,have a closer look at alternator or swap another in if you happen to have a spare.

Per your prior advice, this is leaving connectors DISCONNECTED as I unplug them.

Alternator was working fine and charging, is the 2nd Alternator I've put in this car, and is a used - SE part from my spare engine. Thanks for the advice on how to sequentially hook stuff back up, and will try that tomorrow, as well as Alternator Field Plug, if it will start and run. I would love nothing more than to hear it rev, as it's been weeks without.

On the Alternator ground, I have a spare Negative battery cable run from th Battery Negative post to the adjuster bolt for exactly that reason, to provide a solid ground. I actually removed that today to see if it changed anything. It didnt.

And, thanks. for sticking with me on this fiasco. This is the most frustrating thing,...

All part of owning these old cars and keeping them on the road,helps if you can repair it yourself. Imagine the cost at a shop to fix it,especially if not familiar with 1st gens...

Okay, here's what I found; using advice here, I unplugged everything that I knew had an effect on the Test Light brightness. Inserted a 30A fuse in the Engine location - rated at 20A (*instead of the Test Light), and then started plugging stuff back in;

1) Alternator - Field Connector = Fuse OK
2) Vent / Vacuum Relays = Fuse OK
3) "Circuit Openning Relay, X-07" (aka Fuel Pump Relay) = Fuse OK...
4) Main Harness: "E-F Connector" = Fuse OK for a minute and then started to see smoke while I was poking around. Immediately turned off ignition, and here's what I found when I unwrapped the section of the E-F Connector harness where it goes to the X-07 FP Relay that felt warm to the touch;
http://oi65.tinypic.com/25yu1k2.jpg

Off of the E-F Connector, there's a thin Black Wire, White Trace, Red Dashes that started to melt in several places visible in the photo. I unwrapped this back up the FP Relay harness, and saw where it's crimped to the bigger Black Wire, White Trace, Red Dashes with a brass crimp terminal (factory). The melted portion tells me there's a short on this circuit. I cut the thin wire from the E-F Connector to FP Relay because I'm going to have to repair that wire anyway, and turned ignition to Run (*not Start) - no heat anywhere, and the Fuse was OK.

On a whim, I decided to start the engine. Dash lights looked good (Alt plugged in), Fuse OK, turn key to Start and it fires right up. Runs for 8-10 seconds, but then the engine dies. At least this tells me I have spark, fuel, and air. Now we're getting somewhere (figuratively...)!

Put a meter on the thin black wire I cut, and it's getting 12V to ground. Normally, this would be powering the FP Relay after engine start. A few more start attempts confirms;

A) Fuel Pump is pressurizing the rail prior to start, (I had the test plug shunted at the AFM),
B) Engine Starts and Runs until fuel pressure drops at Injector Rail, and then,
C) As soon as the engine is running, the FP Relay loses signal, shuts off FP and engine dies. Elapsed time, 2-4seconds. It runs longer (8-10s) if you let the FP run a bit prior to starting the engine, but as soon as you hit the accelerator to keep it running, it dies (fuel pressure decreasing, as pump is not running continuously after start).

Progress, but now I'm going back to study the Wiring Diagram to try and figure out what's going on. Bad FP Relay - what Mazda calls the Circuit Openning Relay? I'm almost positive I could bypass the relay and run 12v directly to the Fuel Pump and I'd be back on the road... but that's not safe.

So close,...

Putting a larger than rated fuse in place of correct fuse is always a bad move,whether trying to diagnose a fault or not. Damage other than what is immediately apparent can occur adding more complexity to diag and repair. Hope you track down the source of problem.

this is great advice. i would get a reset-able fuse for trouble shooting so you do not eat through fuses. i use them all the time at work. good luck atleast youre making progess, car wiring can be a night mare until you go over them enough times and learn the lay of the land so to speak

Luckily, it was only a wisp of smoke and I was right there feeling the various harnesses and moving them around so I noticed it right away and shut down the ignition switch. I've since put the 20A fuse back in and it's holding.

Do you have a part # for the resettable circuit breakers? Are they reliable enough to replace a fuse for good?

Thanks again, guys. I'm still studying the wiring diagram for pin #13 on the E-F Connector.

Stay with the fuses,much more predictable and melt more quickly than the circuit breaker kicks out,much like scenario described in above post,you don't want that.

Try running a wire with fuse from the battery to the fuel pump and see if it blows this fuse.

Are you saying just wire 12v directly to the connector in the DS bin - ensuring correct polarity - and see what happens? I can do that, and I would expect it will just spin the Fuel Pump. I can hear the FP running when I use the Test Shunt at the Air Flow Meter, but the problem is that once the engine starts, the Circuit Openning Relay de-energizes, which shuts off 12v to the Fuel Pump, killing the engine.

The Black / White Trace / Red Strip thin wire from the E-F Connector is what energizes the Circuit Openning Relay (i.e., Fuel Pump Relay) after the engine is started and the key moved from Start to Run.

I'm wondering now if I have a short in my Ignition Switch...

Thanks, guys - I'll keep trying these things and report back. I think we're getting close, and my study of the Wiring Diagram @foxed.ca has given me a few new leads which are on the circuit for E-F Connector AND the FP Relay; Starter & Ground, Ignition Switch, and Transmission Harness to look for shorts.

I'll stick with Fuses to avoid causing more problems - and appreciate the ongoing advice.

My thought was that under load, the pump might be blowing the fuse. Isolating the + side would see if the pump is blowing the fuse.

I would put my money on the ignition switch. They are know to get goofy as they age. Has yours ever been replaced?

Ignition Switch has never been replaced / rebuilt.
 

This is one of my next troubleshooting areas (*in addition to the Trans Harness & Starter grounds...), as the Ignition Switch is what carries current for Start / crank and Run conditions for the Fuel Pump Relay - aka, Circuit Openning Relay.

I'm fairly convinced the Fuel Pump ground is bad on one of the harnesses and is trying to use the FP Relay feed as the ground, instead. That tiny wire is only meant to keep the FP Relay closed, not serve as the ground for 3-5 Amps of current flow. Does this make sense?

Fixed!
 

First off, I want to thank all you guys who posted here with advice and things to look for, especially about building a Test Light rig to help me narrow down electrical shorts. The ongoing help kept me focused on troubleshooting, even as my nerves frayed from trying different things, unsuccessfully.

It turned out to be a loose ground at the main engine ground connected to the Starter bolt. This is the single largest negative ground cable in the system, and the nut holding the ground in place was finger tight, but not making good contact. I removed the nut and terminal, cleaned them up, along with the Starter lug that they attach to so that they'd make a solid connection, and then fixed the Black w/Red Trace wire between the E-F Harness and the Circuit Opening Relay. Installed the correct 20 Amp fuse, and turned the key. Fuse held, so turned to Start. Fired right up!

What happened is that the ground at the Starter came loose over time, lost contact as the primary ground for the electrical system, and the Fuel Pump was trying to find ground to carry the load. The only available circuit was through the Circuit Opening Relay (*aka Fuel Pump Replay) where a thin wire ground is used to operate the relay from the E-F Harness to keep the Fuel Pump running. This thin wire ground for the Relay isn't designed to carry that much current and was blowing the Fuse. Connection of the big ground at the Starter restored the primary circuit, allowing the Fuel Pump Relay to function at it's designed voltage and current, and allowing the Fuel Pump to operate using the correct ground which was designed for around 10-12 Amps, max.

I ran the car long enough to warm it up thoroughly and avoid flooding due to short start and shutdown, and it restarted several times in testing the fix.

Once again, my thanks to the board members for your assistance and patience. I've been driving a 1st Gen for 35yrs (an SA and this FB), and this has been the most frustrating experience to locate something so simple as a ground connection...

Its always the simple fix thats the hardest to find. Check yer grounds people!

Glad you got it fixed.

Starter never seemed phased by it...
 

But, yeah - everybody go out and clean up your ground at the Starter Mounting Bolt right now. I'll wait here.

Related but different. I have never replaced my battery cables on my 80 SA. When its really damp and cool out I have been having issues getting the car started.

Raise your hand if you think its the cables? Yeah, I think it is too. I think 40 years out of a set of battery cables is pretty good.

Related, but different - Battery Cables...
 

(Raises hand) I have to admit that these are still the original OEM Battery Cables in my SE, too. I've just never had a reason to change them, and living in the dry desert, there's very little corrosion risk.

I forget who posted the list of AutoZone parts #'s to effectively build new cables from random Battery Cables commonly available, but it was literally about $35 worth of tid bits and done, apart from cutting a section of insulation out of the Negative lead for the body ground at the DS fender apron.

I have installed new Cable Ends several times over the years, though. Might be a good time for that project for both of us,

Also, here's the picture of the SE Circuit Opening Relay (*aka Fuel Pump Relay) for future reference: https://oi63.tinypic.com/19qebk.jpg

My Se has original battery positive and negative cables. There is no reason to replace them. I'm fortunate to be 2nd owner of this car now for 26 yrs. Original owner kept it garaged as have i and the wiring throughout is in excellent unmolested condition.
Sometimes battery cables need to be replaced due to corrosion or physical damage. If the cables physically look good,they can be voltage drop tested to determine how much resistance is in the cable. If they test good,there is no reason to replace them,save your money and put it somewhere else,unless you feel the need for shiny new shi*.
I prefer the original look of oe cables and think enough of them to strip them from cars i've scrapped and come across in junkyards. Not all passed testing but many did,they're keepers stashed in my hoarding room.
So test your cables before tossing them aside for something"new" that you have to cobble together that will look like you did just that. If you have to,you have to...

Good advice Mike. I'll definitely do the voltage drop test before moving forward. Rockauto has decent 4 gauge sets that sell for about $35.00 for all three cables (negative is in 2 pieces).

Got new cables coming in. I used a battery tender to top up the battery to 13.30 volts on my cheapo HF meter. I then started the car no problem, did a run and came back to the garage. I measured the output from the alternator with + on the B terminal of the alternator and - on the battery post. It showed the alternator putting out 13.80 volts, seems good to me. I then put the + over on the batter terminal and it only measured 12.90 volts going to the battery. I think its safe to say theres a dropped there that shouldn't be there and its probably on the positive cable side. So, new cables and cleaning up all the connections is coming up this weekend. Also adding a extra ground near the alternator on the block to help charging and ignition.

LongDuck, sorry I thread jacked you but thought was useful info.

Just reading your post Tim,not type voltage drop test i was suggesting and we were talking about battery cables in that post.

Back to what you just posted..13.8 at alternator and 12.9 at battery. Definitely have something going on there almost 1 volt drop and possibly not battery cable at all. Set your voltmeter up like you described,running car,13.8 at alternator and start working your way back from alternator and follow harness back to main fuselink area and check voltage there.What is it? If it's measurably lower at that connection than at alternator,you have resistance in that section of output wire and/or the connections at each end. If that 13.8 reading follows to that connection then the problem is in the feed wire from battery to fuse link. Check the connection of power wire at fuse link for corrosion or overheating and then work your way back to the battery connection for main feed wire looking for faults.

A solid electrical system that shows 13.8 at alternator(that should be 14.0-14.3 volts at alternator with car running and nothing on)should show less than .5 difference at battery,that's 13.3 and that's initially too low before you start turning accessories on.
Find that 1 volt loss in circuit and you will see that in your headlights at night,it'll look like you put brighter bulbs in.Wipers run faster as well as heater motor,dash lights brighter. I believe you're running an FC alt,your car is definitely not getting near what that unit puts out.

Regarding battery cables...or any circuit you want to voltage drop test. You need to load the circuit,make it work while you're testing it. To test battery cables,disable ignition so car cannot start(fully charged battery) put positive lead of voltmeter on positive battery cable and put negative lead of voltmeter on battery cable lug at starter. Crank the engine and note the voltage reading displayed on voltmeter,what it registers will be the voltage lost from beginning to end of that circuit(wire). Same,same for negative battery cable. Test your cables and post back what you find-before you replace/disturb anything. This is your base line. When done repairs,retest. You can get an exact voltage drop reading in wire from alternator to main fuselink and from there to battery feed for main fuse link the same way. Car running,pos lead of voltmeter on alt output post and negative lead on car side of main fuselink. Identify your problem areas,you don't have to replace everything to improve anything...

post #1 said that ....u live and learn... i ground everything twice...... :rolleyes:

i'm glad u figured it out.....hope u didn't push any gray hairs out

The irony was not lost on me on finding it!
 

Thanks for posting it, and the admonishment about getting grey hair chasing electrical gremlins that are more easily solved by looking at the grounds! I did learn a lot about the wiring diagram, and who knows how that may come in handy in the future. Thanks to all who helped out,

Mike, I did the lazy test and got lucky. I know what you mean about voltage drops methodology but I just wanted to check basic charging health and this is an easy way to verify it. Turns out I cleaned the ground connection on the fender strut area and traced the high voltage lead from the B terminal to the engine harness connection below the master cylinder. There I found the lead goes around the main harness connector and connects via a large 1/2" spade to another lead into the main wiring harness back into the chassis. Hmmm, I thought to myself, can't hurt to clean this up either. Did that and measured again and had zero drop from the same measurement point while engine running. I just did a drive from Charlotte to Raleigh and back yesterday. The battery was charged to 13.03 volts which it was never getting to before. I still will replace cables and clean up connections on and around the starter and place that extra ground to the front of the block from the fender as well. I have to admit, I did neglect this area for a long time. If it ain't broke don't fix it kind of thing.

Maybe I should write this up in its own thread with my new ground wire install (wires from rockauto) just so folks can easily see all the details. Gems of information sometimes stay buried in various threads and I think its valuable to pull them out and summarize some of them.

Copper is copper, it's not really going to "wear out" per say. The protective casing will dry out and crack after many years of heat cycles and flexing from the motor moving within its motor mounts. The terminals will corrode but can be cleaned up with sand paper, a wire brush, a wire wheel, etc. As others have said, follow the electrical path from the alternator bolts, to the transmission bolts, to the starter, to the ground point to the battery. When replacing any of these components it's good to clean off the mating surfaces and wash the bolts of non conductive grease and buildup...and if you painted your engine during a restoration, you'll definitely want to scrape/sand/wirewheel off the paint where the alternator mounts, especially true for any side-mount brackets too.

With that said, I did just replace mine with 2ga high-strand count wire. I'm not sure what gauge the originals are, maybe 4ga? I used some plated wire terminals too. Haven't started the car yet, but I verified the starter motor does work. Jump to post #92 of my build for pics...
https://www.rx7club.com/build-thread.../#post12333857

True copper doesn't "wear out" but the package as a whole degrades over time. That weakening of the covering starts letting moisture in. That causes corrosion. The corrosion can cause resistance. Resistance reduces the amount of current that can flow. I think it's safe to say after 40+ years, new wires may be in order. Consider this, I didn't have this issue until the recent very damp spells we have had all winter here in Charlotte, NC. Moisture in the air appears to have been some of the culprit here.

Mike, you are correct in that my wipers do work much better now. My fuel pump is noisier too as it sounds like its pumping harder.