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Wiring thought

Old 06-10-09, 01:57 AM
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Wiring thought

Working on trying to simplify the race car. What is the absolute minimum wiring, switches and fusing needed to start the car, charge the battery, and run it? Considering a completely stripped out interior, minimal gauges, no need for lights, what is the minimum needed to run a second gen seven?
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Old 06-10-09, 04:04 AM
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The minimum needed would probably be to strip out everything, and then hook up and run new wires only to which components you reinstall and feel are neccessary.

You really only need to run an engine... but headlights and a speedometer make it partially street legal.

Your question is pretty vague at best though. Do you have any experience in tearing apart wiring harnesses for a desired effect?

What is your goal with this car?

Is it still going to be street driven?

Is it going to be used for sanctioned racing of some sort?

Don't sacrifice another car to the unfinished-project-gods just to improve your power to weight ratio slightly.
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Old 06-10-09, 08:41 AM
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First big question - stock EFI or carb?

Second question - how much time/pain/money are you willing to spend on this?

(is this for an FD, FC or FB?)

If carb - you can really simplify the system. Look through the Summit catalog for the Painless harnesses. At this point you are probably going to want to ditch the stock console and go completely aftermarket gauges, if you haven't done so already.

If EFI - not worth the effort unless you already have major harness issues. If you want to, lightening and repairing an existing stock harness (aka. "the wire diet") is probably your easiest route.

In either case, it is a lot more work than initially meets the eye. Think about things like wipers, running lights (you may want to keep your head lights if you plan on running in the rain), fuel pump and relay, charging system, ignition system.

Just look through the FSM at the harness diagrams and note everything you need to keep. This should give you an idea of what you will need to do.

Good luck,

-b
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Old 06-10-09, 10:23 AM
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Sorry should have been more specific. Started with and 87 Sport model that the interior was shot after sitting outside with broken windshield for 6 years. Will be SCCA Solo2 F Prepared. Will have Megasquirt for fuel and ignition. Will never be street legal or even want it to be. Been chasing way too many shorts and broken wires recently so wanted a fresh start with good wires. I am fairly competent at building cables and reading diagrams. And willing to dig into most anything.

My weak areas are the obscure areas of auto wiring such as what needs to be fused and what doesn't. What needs to have a relay and what doesn't. And what the heck is the ballast resistor pack used for. Again, I don't mind digging into almost anything.
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Old 06-10-09, 10:34 AM
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If your planning on building your own harness its not tough at all with basic knowledge. As far as fuses go, Fuses are used as circuit protectors. Used on power sides of the circuit. Usually on found on Computer, and Electric motor power wires. Most wires with 12v in them should be fused. Those are the ones with the most potention to burn up because of the current these circuits can pull.
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Old 06-10-09, 11:16 AM
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And relays just offer a way to control a circuit without having to make the circuit thats being controlled extremely long (the longer a wire is the more potention for resistance in that circuit). If that makes any sense. When the relay does not have power and ground at terminals 86 and 85 then terminal 30 is connected to 87a. When you add power to 85 and ground to 86 terminals then the relay actuates like a solenoid and now terminals 30 and 87 have continuity. So by applying terminals 86 and 85 with power and ground you control the circuit that is ran through 30, 87a, and 87. So with this relay you can connect 12v power to 86, and have a Wire coming from 85 to a switch and from the switch to ground. So when you actuate the switch u control ground to the circuit with in return controls the cricuit that passes through 30 and 87.

86,85 circuit not energized

86 ------85
.......||.....
.......||..... 87 a
30 ------/
.................87

86,85 circuit energized

86 ------85
.......||.....
.......||..... 87 a
30 ------\
.................87


Note- Circuit 30and87 are not electrically connected to the circutit between 85and86. Theres a rod that pushes a switch internally.

Im sure i made that much more confusing than it should be. But im bored at work.
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Old 06-10-09, 12:22 PM
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Originally Posted by Handful View Post
And relays just offer a way to control a circuit without having to make the circuit thats being controlled extremely long (the longer a wire is the more potention for resistance in that circuit). If that makes any sense. When the relay does not have power and ground at terminals 86 and 85 then terminal 30 is connected to 87a. When you add power to 85 and ground to 86 terminals then the relay actuates like a solenoid and now terminals 30 and 87 have continuity. So by applying terminals 86 and 85 with power and ground you control the circuit that is ran through 30, 87a, and 87. So with this relay you can connect 12v power to 86, and have a Wire coming from 85 to a switch and from the switch to ground. So when you actuate the switch u control ground to the circuit with in return controls the cricuit that passes through 30 and 87.

86,85 circuit not energized

86 ------85
.......||.....
.......||..... 87 a
30 ------/
.................87

86,85 circuit energized

86 ------85
.......||.....
.......||..... 87 a
30 ------\
.................87


Note- Circuit 30and87 are not electrically connected to the circutit between 85and86. Theres a rod that pushes a switch internally.

Im sure i made that much more confusing than it should be. But im bored at work.
NP, I understand relays in general and why they are used. So only thing I have left that I do not understand and could not find in the FC wiring diagrams is the Ballast Resistor pack so I don't understand how and why it is used. Is it used in the starter circuit for protection or is it used in the ignition system for something? I have seen references on the net for ballast resistors tied to starters, and others tied to ignition coils. Currently I will be using the stock coils.

By the way, really appreciate this discussion. I have decided to reuse as much of the current fuse panels as possible, but will most likely move them to more convenient area. Just splicing in my new wiring where needed while getting rid of the oil soaked, mold infested old harness.
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Old 06-10-09, 12:30 PM
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have a look at the wiring diagram, and then look at it system by system. most things are very simple.

i like to build mine like the factory would have, and wire it up like they did, except i just remove things.

this also makes it easier to troubleshoot later.

when i got my current FB it had a 100% custom harness, the front was all red wires, the rear was all black wires. plus they used big fat wires, and tons of zipties and scotch locks and things.

the factory harness was like half the weight of this thing
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Old 06-10-09, 02:25 PM
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hase anyone used a sumit or like kind fuse box/ wire harness, and if so how did they like it. i have 12a living in a 912, thinking of ditching the existing wiring and have the minimums.
also, off topic, whats the best carb for a daily driver with minimum tuning requirementz? the 12a i have has a old 650 holley (not my choice) and drips, not sure if its to much pressure or dried up seals
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Old 06-10-09, 03:56 PM
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Originally Posted by simonrex55 View Post
hase anyone used a sumit or like kind fuse box/ wire harness, and if so how did they like it. i have 12a living in a 912, thinking of ditching the existing wiring and have the minimums.
also, off topic, whats the best carb for a daily driver with minimum tuning requirementz? the 12a i have has a old 650 holley (not my choice) and drips, not sure if its to much pressure or dried up seals
Might be time to rebuild the carb if its leaking. But i know, The Holley's I use to use on my V8's were notorious for leaking fuel. I duno what kind of intake the 12a's have. But if its like the V8's i always liked the Edlebrock/Carter style carbs. 2 pieces top and bottom, shouldnt have trouble with leaks and virtually maintenence free. But again i dont know much about carbs for the rotory.


Also for the wiring harness. Dont use cheap electrical tape to tape one up, and dont stuff it all in the conveluted tubes. I know here at the International Dealership we sell a really nice cloth harness tape that I use on all the harness i repair. I would recomment that stuff if your gonna wrap a harness.
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Old 06-10-09, 05:01 PM
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Originally Posted by Handful View Post
Might be time to rebuild the carb if its leaking. But i know, The Holley's I use to use on my V8's were notorious for leaking fuel. I duno what kind of intake the 12a's have. But if its like the V8's i always liked the Edlebrock/Carter style carbs. 2 pieces top and bottom, shouldnt have trouble with leaks and virtually maintenence free. But again i dont know much about carbs for the rotory.


Also for the wiring harness. Dont use cheap electrical tape to tape one up, and dont stuff it all in the conveluted tubes. I know here at the International Dealership we sell a really nice cloth harness tape that I use on all the harness i repair. I would recomment that stuff if your gonna wrap a harness.
Going to use heatshrink to make subharness, then the cloth tape for the final wraps to it can take the abrasion better. Heat shrink will add strength and still be flexible and make for neater bundles I hope.

OK, specific question, I still have not found where the ballast resistor pack gets wired in or can I just not worry about it with the stripped down harness and needs?
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Old 06-10-09, 05:21 PM
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I think its has to do with the Injectors. My buddy had to make one when he he swapped a t2 motor into his FB. Im probabaly way off, do some research.
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Old 06-10-09, 05:25 PM
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Originally Posted by Handful View Post
I think its has to do with the Injectors. My buddy had to make one when he he swapped a t2 motor into his FB. Im probabaly way off, do some research.
I'll dig in that area, never thought about looking around the injectors. Thanks, I'll post what I find for others.
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Old 06-11-09, 11:10 AM
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Update on the ballast resistor that I have been trying to find. The only place I see it is on the wiring diagrams for the Turbo engines and it appears to be labeled "Fuel Pump Relay and Resistor" on page 50-34 of the wiring diagram. The location chart, and connector layout match what I was looking for. So since I am wiring a Non-turbo I should not need to put this back in. It is interesting how many things I have found in this car that are supposedly for a turbo only. I know this car has never been modified before I got my hands on it as I got it from a friend who does not work on cars.

I will be getting back to the actual wiring tonight if my work schedule allows.
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Old 06-11-09, 11:12 AM
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Originally Posted by bschnard View Post
FC wiring diagrams is the Ballast Resistor pack so I don't understand how and why it is used. Is it used in the starter circuit for protection or is it used in the ignition system for something? .
WTF are you reading? ballast resistors were used to drop the power to the ignition POINTS, when the car was running so they would last longer. there is usually a switch/relay to bypass these during starting

the last mazda to have something like this was the 79 rx7, everything after that is solid state and can run on 12v.
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Old 06-11-09, 07:17 PM
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Originally Posted by j9fd3s View Post
WTF are you reading? ballast resistors were used to drop the power to the ignition POINTS, when the car was running so they would last longer. there is usually a switch/relay to bypass these during starting

the last mazda to have something like this was the 79 rx7, everything after that is solid state and can run on 12v.
Well I obviously had my head where the sun don't shine. This is not actually a ballast resistor as I thought, but is wired between one side of each injector and the ECU. I am still chasing that end down to make sure. I actually dug through the old harness to chase this.
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Old 06-12-09, 07:11 AM
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Search for "low impedance injectors". These were used on S4 cars (not S5). The resistor pack was used to allow the ECU to safely drive the injectors. If you are going with a new ECU, then ditch the low impedance units and go with a set from an S5.

If you going with a Mega-squirt from www.diyautotune.com, use their ECU harness and then go with a Painless harness (http://www.painlessperformance.com/) for the rest of the chassis electrical. You can roll your own, but it sounds like you would be more comfortable with something a little more cook-book.

There is some good information on car wiring over at the Locost builders site in the Electrical and Wiring sub forum. Go to http://www.locostusa.com/forums for more info.

Here is a warning: reharnessing the car is not as cheap as you would think. Still less $$ than new stock harnesses, but there is a lot of work involved. Some people find it to be a very Zen-like experience, others end up tearing all their hair out.

Good luck,

-b
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Old 06-12-09, 07:41 AM
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Originally Posted by j9fd3s View Post
when i got my current FB it had a 100% custom harness, the front was all red wires, the rear was all black wires. plus they used big fat wires, and tons of zipties and scotch locks and things.
Good point - no matter what you do, use different colored wires!! There is a reason that the industry (not just auto but across the board) does things this way.

[someone will now probably mention that military and aviation harnesses are not this way and tend to be all one color, but that is because the entire harness is usually a field replaceable unit (FRU) and rarely needs to be debugged while in place.]

-b
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Old 06-12-09, 10:07 AM
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Originally Posted by wrankin View Post
Good point - no matter what you do, use different colored wires!! There is a reason that the industry (not just auto but across the board) does things this way.

[someone will now probably mention that military and aviation harnesses are not this way and tend to be all one color, but that is because the entire harness is usually a field replaceable unit (FRU) and rarely needs to be debugged while in place.]

-b
Well I am using the MegaSquirt harness for that part of the car, it is already done. I am adding battery cut off switch which is almost completed, going to reuse the main fuse panel and the MS relay board. have that wiring started and should finish that tonight. My only real sticking point was that resistor pack for the injectors that I just do not see in any of the wiring diagrams so that had me stumped as what it was for but I was pretty darn sure I should keep it.

The budget won't allow new injectors right now so I will get new resistors and put them in series with the injector leads going to the relay board per the MS subforum threads I have read. However when the budget does allow I will go for S5 injectors.

I am going for absolute minimum in wiring so only tiny amount of additional wiring other than what I have detailed above and already have that drawn out as to what to do.

Oh, and I have had experience with all one color wiring in military aircraft, and I spent more time than I care to remember chasing wires and repairing connectors.

Thanks again for the added advice. I have learned a lot from this discussion and that is always a good thing.
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Old 06-12-09, 01:56 PM
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Originally Posted by bschnard View Post
The budget won't allow new injectors right now so I will get new resistors and put them in series with the injector leads going to the relay board per the MS subforum threads I have read. However when the budget does allow I will go for S5 injectors.

.
just reuse the resistor pack you have, feel free to mount it anywhere you want
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Old 06-13-09, 03:51 PM
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By the way, went to locostusa link, great site, lots of good info.
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Old 06-16-09, 03:57 PM
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Get rid of the stock key switch - and use dedicated new switches for each circuit.
Old stock switches = corroded contacts = voltage loss
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Old 06-17-09, 03:35 PM
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Yep. all new switches, main fuses moved to cockpit, getting real close to initial flip of the battery cutoff switch. If you hear sirens I might have made a wiring mistake. LOL. Before I do anything will go back over everything with ohm meter to check for obvious mistakes. I hope to have the first test sometime Saturday.
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