Charging Problem: Alternator? Charging Harness?
 

I've eaten a couple batteries, an alternator, and fried my charging harness over a few years. Rick spliced my charging harness a few years ago and I thought it was fine. A couple months ago, I left my dome light on and ran my battery dead, but I put it on the charger and it seemed to come back. Went on a month's vacation and it started when I got home.

Today I met a fellow rotorhead and after parking the fans came on, and when I went to start it was dead. We jumped it, but it barely made it home and all the dash lights went out. Reminds me of a bad alternator I had on a truck years ago.

Maybe I hurt this battery beyond what the alternator can do. It's labeled 8/19. But, it felt strong this morning. She started really strong. And, it ran great last night.

I wonder if I have a bad charging harness, or a bad battery, or a bad alternator. Or, some other short I'm not thinking of. I do notice some voltage leak through my interior lights (my ash tray light is lit dimly even when I have the lights off, I thought it could be the TNS(?) relay or it could be coming back through earth, I guess).

I'm trying to go on a big road trip to socal Saturday, so I'm on the verge of overnighting a new charging harness. Any ideas about what to check are appreciated. I have all the manuals and can figure stuff out, but worried I can't do it in time to make JCCS.

I'm gonna go get a new battery now, since that's super easy.

There is an easy way to test both Battery and Alternator with just a voltmeter. Plop the leads on the battery terminals and read the voltage in the following states:
1. Key OFF: 12.6
2. Key ON: 12.5-12.6
3. Cranking to Start: 10.0 or more
4. Engine Running: 13.5-15.0

If ANY are low, charge battery and re-test with the following stipulations. If 1 is fine, but 2 is low, bad battery is suspected. If 1 and 2 are good, but 3 is low, bad battery is suspected. IF 1-3 are good, but 4 is low, bad alternator is suspected. Remove the suspected part and bench test it. If it passes a bench test, your harness is the issue.

I don't know who this "Rick" is, but there is only person here whom I would allow to do any wiring on anything I own. It's the person who taught me, and that is Aaron Cake.

Before you make a knee-jerk purchase, let's see your harness in question first.

Old battery is on the charger and it's definitely wounded. But, that could be from running with a bad alternator. Rick from Rick's Rotary in Pleasanton. He's closed shop now, and it wasn't my favorite fix, but it beat an $800 harness and seemed to hold.

Got my multimeter ready, will report back.

Feh. Battery not getting enough charge. Deeper we go. Probably fried the alternator on the bad battery. Hopefully the harness is cool.

In better news, I don't see a major current leak with everything off. Looks like about 15 milli amps. Sounds like that is within acceptable limits.

So the battery charger gave the alternator a frowny face. Checked it with the multimeter. I get 14v across the battery poles when engine is off. When running I get a little better than 13v. When I turn on the fans and lights, I can see it start dipping around and under 13v.

I think the original alternators are getting tired, and possibly the original wiring harnesses too. My car's alternator died last year after sitting outside in freezing temperatures. I suppose another way to view it is the thing survived over 97000 miles and 27 years. Most cars see more miles, but still get scrapped before they are 25 years old. I got an upgraded alternator from IRP, but since then I've heard a handful of RX7 owners complaining about inconsistent performance from IRP alternators. My plan is to start checking alternator voltage carefully in ECU datalogs and switch to a new one from DC Power if it looks inconsistent.

Most medium or large cities should have at least one shop that can bench test and rebuild alternators, that might be looking into.

Forget the volt meter for now. You need to load test the capacitance of the battery. I’ve seen batteries read 12.5v but fail the load test. Even one year old ones. To quickly narrow it down if you need a harness for your trip, take the alternator off. Take the alternator and battery in question down to your local autozone / advance auto ( battery supply places can load test the battery but won’t normally have alternator testing ) and have them test both. Normally they do this for free.

Moving foward, after you know you have a good battery and alt, assemble everything and test the resting voltage of the battery cold. Start the car and retest immediately. Let it warm up fully and test again. Post your results.


I just realized you’re located in Dagobah. So you might not have an autozone local :)

~ GW

First off, a battery isn't going to hurt or damage an alternator. If you hook up the battery backwards all bets are off (that just breaks WEIRD stuff).

As stated all you need is a multimeter to troubleshoot this. One report you had showed very high (14v) on the battery, it's common for the battery to have a high voltage after being on the charger but that will fade down to the resting voltage of around 12.5 or so.

If you really suspect the battery, take it to an auto parts store. They can do a load test on it to see what voltage it has under load (like cranking). They should be able to give you a solid Pass or Fail on it.

Some auto parts stores can test alternators, but I have actually had an alternator damaged once on one of those tests - blew a diode. Again the multimeter test will tell you for sure, but if you are getting under 13v (which it sounded like you were) I'd replace it. The stock alternators seem to give up around the 100,000 mile mark FYI.

https://www.rockauto.com/en/moreinfo...OUBypvpAOj3Ovd

^That is a fine stock replacement. There are aftermarket higher amp ones and stuff but IMHO there's no reason to get carried away unless you truly need it.

Dale

Modern batteries can be irreparably damaged with being totally drained one time. Used to be, batteries were more robust, but maintenance-free batteries are not happy with being run flat.

I replaced the battery yesterday with a brand new one, and for now the car seems much better. This alternator should only be a few thousand miles old, since it replaced the original one a few years ago.

My battery charger has an alternator test feature, which returns negative results. Sadly, that's literally all the information it gives. It basically returns alt-bad or alt-good with no other info.
The multimeter shows voltage under 13 when I run the fans and lights. It has an analogue readout, so I'm calling it like 12.8v from my eyeball.
I might go get a digital multimeter today. I'll drive the car around and maybe that would help reveal if it is still having any issue after replacing the battery.

It looks like Atkins has the charging harness and alternators in stock. And, both are pretty easy to replace at home.
It's strange that this car melted the original charging harness at the alternator side and needed and new alternator(~2019).
About the fans, I replaced my original fans with the Rx8 fans and re-pinned the connectors. I ran a smoke test last night and it seems they're both pulling air. I'll take a close look today, in case they are part of the issue.

Thanks for all the help. Will keep y'all posted. T-minus 5 days 'til JCCS.

I would look for an auto electric shop, you can usually find them by searching for places that can rebuild alternators and starters. The guys working the counter at an auto parts store are less likely to know how to use the alternator testing equipment properly.

If you need a new battery, I vote to spend the extra on a sealed AGM one to avoid the possibility of leaking acid. I'm super bitter about the last time I had a lead-acid battery in my car, I had run AGM batteries before but but went with a cheap stock-sized one to save $50 or whatever it was. I spent many hours cleaning acid, and it will still need to be repainted some day.

https://cimg2.ibsrv.net/gimg/www.rx7...1503e678a6.jpg

Ran down another battery driving. Limped home with no lights. Alternator and/or harness have to be dead. Ordered new ones from from Atkins. Hate to do it, but multiple indicators point to a bum alternator. Multiple resources indicate a bad battery could fry an alternator. Here's a random one: https://ricksfreeautorepairadvice.co...ator-failures/

A reman alternator isn't the most perfect thing on earth, does sound like you got a bad one. I'd get the one at the link I provided and replace it.

I wouldn't go messing with the starting/charging harness until you are SURE the alternator is happy and is good.

Dale

My thoughts exactly. Never assume anything is good until it is proven to be Known Good. Plus, while FD alternators aren't as fail-prone as FC ones, Mitsubishi's record of taking shortcuts is well known. Just ask Aaron Cake about the Cosmo's "60A" alternator that would do 40A on a good day. Based on that, I'm thinking they're measured in chinese amps. Maybe they should add some stickers, I heard each one adds 5hp...:lol:

On my 20B FC, a FD Alternator couldn't feed a Taurus fan on Low (~20 amp draw). Difference between a S4 Alt and FD Alt is 20A, so the car would behave like a stock S4 with an underpowered alternator as they are all guaranteed to do. Conjecture aside, the idea of leaving a known failure point does not sit well with me, especially when a solution is readily available. That's why I ended up with a Ford 3G alternator from a junkyard 3.8L Taurus that will do 80A all day at idle. And using the Ground to Test terminal, it's enough to trip a 150A 12v circuit breaker in the passenger side bin through 17ft of 4awg cable At Idle. And given the Voltage Drop per the following calculator, I'd wager it was probably putting out around 170 amps.

https://www.calculator.net/voltage-d...y=20&ctype=nec

Did some more math and since it was at ~15v at the time instead of 12v, it ends up being 2250 watts (15 volts x 150 amps). Factor in the Voltage Drop (1.59v lost) from above and it calculates out to 167.79 amps seen at the circuit breaker, so I wasn't too far off in my guess. Plus, they're common as dirt, new brushes/regulators are cheap and anyone's Uncle Jimbo can rebuild it with a screwdriver set and a few toothpicks thanks to the million demos on Youtube.

If you have the space for it, and the fab skills for two simple flat adapter brackets, why not retrofit one? That, plus a Deka Intimidator AGM battery and some properly made cables, either crimped or soldered, and it'll live forever.

Hmm. I like to use stock stuff where I can. But, I have considered aftermarket alternators. I've converted almost everything to LED and I don't have a big radio. The fans should be the biggest draw on the system. Maybe the fuel pump and ignition system. A good stock alt should work for me. I've got a couple on order. I guess for all the money, I should have gotten a real nice aftermarket one. Hopefully the stockers get me down the road and we could revisit later.

The AC Delco “reman” from rock auto Dale mentioned is a quality piece. Installed one on a friends FD recently, it looked like all brand new parts were used including the pulley and it outputs a stable 14.05 - 14.1 volts regardless of engine speed or electrical load. Idle with everything on, AC max fan speed, rear defroster, lights, was 14.05v. Rev it up it’s 14.1. Turn off everything it’s 14.1. Very stable. Couple of things, the unit we received had a very slightly larger pulley compared to stock (belt still fit) but rotational speed will be slightly lower (not a bad thing considering the output), also the main battery connector was a slightly different shape but the cable still fit fine. AC Delco is the way to go if you need a replacement FD OEM style alternator IMO. Reasonably priced and gets shipped quickly.

I had a (somewhat typical) bad alternator experience with my Chevy Van tow vehicle. As preventive maintenance, at 190K miles I replaced the OE alternator with a reman. It lasted 10K miles before it seized its bearings in the middle of a trip. I had to put the removed OE alternator which I kept as a spare back on.

So it shouldn't be a surprise when a reman craps out.

I do want to point out that for 90% of FD owners a stock or stock reman alternator is all you will need. Don't get too far into the rabbit hole of upgraded alternators, most times it won't do your car any favors.

Even my car which is fairly well modified has a stock alternator and does great with it.

Dale

Reading thru this post about alternator woes, it reminded me of the headaches I was having with my FC, that started after going to a full aftermarket engine management system, E-fan, upgraded fuel pump, IGN1A coils, etc.. Anyway, my FC was killing "high output" reman alternators at a fast pace, so I decided to get some measurements of full load current draw to characterize what was going on, and how much alternator output I really needed. Below is my post from the other RCC forum, cut & pasted in its entirety for reference here:

After another "110A/high output" alternator took a dump just 4 months out of warranty, I decided I needed to find a way to measure charging current to characterize my FC's charging needs as various loads are switched on & off. I found this little gem on Amazon for about $17 shipped that does the trick:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Basically it's a hall effect current sensor ring that you slip over the B+ alternator charging wire. They have 100A and 400A versions; I opted for the 100A version. You wire power to the little circuit board, either via a 9V battery or hard wire it to the car's 12V switched supply. Since I didn't want to permanently install it, I went the 9V battery route.

The resolution on this sensor is rather course, about +/- 0.2A per spec for my 100A version, which is useless if you want to use it to help find parasitic loads/shorts when the key is off, but was fine for my purposes - charging current characterization where +/- 1A resolution will do.

After installing my new 110A alternator, I installed the sensor ring, and temporarily mounted the display/battery to the dash and went for a drive. Here's a few observations:

- For the 1st few minutes after starting the car, current draw is much higher than what I was seeing as "steady state". Steady state for my car (no additional loads, but engine running) was around 18~20A. Same loads but within < 5 min after start, and I'd see about 50A. I attribute this to the fact that on start, the battery discharges a bit, and the alternator is trying to bring it to a fully charged state ASAP. During this higher current draw period voltage will read 14.5V, and will drop to about ~13.6 as the current draw drops to its steady state 18~20A figure.

- Whenever my main e-fan kicked on, I saw a brief 20A inrush (added to whatever the steady state was), which dropped to about 10A while fan is running. Oddly enough, just the brake lights impose a similar 10A load, with much less of an initial inrush current. Think it's time to replace all those halogen bulbs with LED equivalents!

- Full boat current draw on my car at idle, with AC on max, main E-fan & stock Aux E-fan running, headlights, fog lights, brake lights + rear defroster on was 95A. So it would seem my new upgraded 110A alternator is keeping up, but there's little headroom there, which explains the short life. Bottom line lesson learned is that I need to (a) Reduce electrical loads where possible and re-measure loading, and (b) If after reducing electrical loads (LED lighting, etc) gets max load below the point where I have a 25~35% margin with the 110A alternator, do nothing. Otherwise move up to a 130~150A rated alternator.

What you report in terms of initial current draw and then steady state is textbook behavior. I opened up the workshop manual, which details similar load testing. I half regret not going through the diagnostic steps, but I'm time limited.

Alternator is currently out, next the harness. Will report back. Wish me luck, please.

Welp. I got the battery harness and alternator swapped in, just in time to make a run for JCCS.

Unfortunately the new alternator was worse than the old alternator. It appears to have a bad voltage regulator, and destroyed two batteries. One I started with, and one I tried to limp back with. Read 18v when we tested it at autozone. I really wish I had put the multimeter on it before taking off.

Anyways, I have one more spare stock alternator to try. I'm gonna clean all the grounds and try again. 3rd time is the charm?

Suggest you order an AC Delco "reman" alternator from rock auto. It will work.

https://cimg3.ibsrv.net/gimg/www.rx7...83ddc21f4.jpeg

Welly, welly, welly, welly, welly, welly, well. To what do I owe the extreme pleasure of this surprising visit?

Misery loves company!
 

Looks like I'm joining the dead alternator club on my FD now. I'm finding that the one it came with is getting weak whenever the engine bay heat soaks - so after driving around for a while, then getting stuck sitting in traffic I'll notice my voltage dropping below 13.5VDC, and if I'm running a bunch of high-amp loads (A/C at max, fans running max, lights on), it will dip as low as 12.8V at a low idle. Bumping up the idle a bit helps with that, but at only 13.3V~13.5V it's barely charging the battery.

I guess I'll be dropping in one of those AC Delco units too. Which sucks because the OP had the old alternator case powder coated to match the intake mani and some other engine bits :banghead:

@Pete_89T2 Welcome to the party! If you really wanted to, you could swap the case over. The FSM has a good diagram of disassembly.