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Running alternator in FC without stock wiring harness

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Running alternator in FC without stock wiring harness

Old 05-05-08, 04:59 AM
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Running alternator in FC without stock wiring harness

We have an FC race car that was converted to carb and subsequently had the wiring harness taken out of it, and rewired as simplistic as possible, with no dash/warning lights.

It doesn't seem our alternator is charging though. We have the charge wire hooked to it, but there is another plug on the back that according to the wiring diagram one post gets 12v from ignition, and the other goes through the warning light relay and then to ignition, but we don't have this relay.

Does anyone know why the alternator may not be working? We tried hooking up the 12v ignition portion of that plug to the ignition toggle, but no dice. Does the other plug need a straight 12v or does it need a relay/diode in there?
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Old 05-05-08, 11:58 AM
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That plug is exactly why it's not charging. I ran into that myself.

I ended up just sending it 12V from an ignition hot source and that solved the issue.

PaulC
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Old 05-05-08, 11:59 AM
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mmm, then I'm not sure, we solved it with 12V to the plug, but I did notice the S5 alternator didn't charge with 12V at the plug, but the S4 one does. Didn't bother trying to figure out why. If you do find out let me know.
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Old 05-05-08, 08:38 PM
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So do we need to put 12v to both posts, or just the top one?
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Old 05-12-08, 08:11 AM
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Ok, so it is definitely an S4 alternator, and do I put 12v to both posts on the back plug to make it work? Power to one post (top) isn't working.
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Old 05-13-08, 12:06 AM
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just pick up a one wire alternator. all you have to do is run you alternator wire, which you already have, and your done. or you can have the voltage regulator changed in your factory one and have it converted to a one wire set up. if you go to any auto electric shop they should be able to do that for ya.
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Old 05-13-08, 10:52 AM
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Good idea. Thanks!
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Old 05-13-08, 12:30 PM
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no problem. i had the same dilemma when i installed my microtech and i just switched to a modified gm 100 amp one wire alternator. works just fine but you gotta grind on the mounting brackets to make it work
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Old 05-14-08, 04:01 PM
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I just have key switched power going to the 1 wire on the plug no problems charges fine. I cut the other wire off.
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Old 05-18-08, 04:14 PM
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Originally Posted by Rotary-Celica View Post
I just have key switched power going to the 1 wire on the plug no problems charges fine. I cut the other wire off.
Top wire, or bottom?

We put the power to the top wire, it didn't seem to work. We put it to both, and the ignition switch no longer cut power to the ignition box. lol Had to shut off the fuel and hit the master kill.
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Old 07-19-11, 08:48 AM
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Thumbs up

I noticed this is VERY old but I wanted to chime in for future reference.

I'm re wiring the car because it is also a carb'd FC and I want to utilize the stock switch and turn signal system for when I have to drive it to the event (since its still road legal)

my old harness has been hacked apart and just ugly for years but I run an FD alternator on my S4 chassis, I have just run a fuseable link from the S terminal to terminal B with my molested harness.



I dont use the L terminal at all.

Haven't finished the rewire but we shall see how the S to B+ works out soon enough.
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Old 07-19-11, 11:16 AM
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I had issues with non-stock harness charging and fellow racers blowing alternators.

I purchased a GM small body 100a single wire alternator and a dual belt pulley and never looked back.
Very easy to install in the stock location with no space issues. In fact, you can install a full size alternator in stock location w/o issue.

The problem with installing these alternators in this fashion is they don't like backfeed which is what the idiot light relay is there to help do. It feeds a constant resistance with no backfeed voltage.

If you put a bosch relay on the "L" terminal, it will help with charging with little risk of regulator failure.
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Old 07-19-11, 12:02 PM
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Then would I just wire the L terminal to the pin 87? Then hook up the other terminals 85, 86, and 30 as normal.
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Old 07-20-11, 07:40 AM
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Its been a long time but i think I had mine hooked up like this:

85 - L Terminal
86 - Ground
87 - Idiot Light +ve (ground other lead)
30 - Hot on ign

This way, it uses the coil of the relay as a constant resistance to "excite" the rectumfinders.
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Old 07-20-11, 05:07 PM
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How long are your races? A carbed car can run for a while without an alternator. I used a stock idler pulley from the AC belt adjuster and got rid of 11lbs on top of the engine. I run a bigger than stock battery in the area behind where the pass seat woul be.
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Old 07-20-11, 05:27 PM
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Originally Posted by jgrewe View Post
How long are your races? A carbed car can run for a while without an alternator. I used a stock idler pulley from the AC belt adjuster and got rid of 11lbs on top of the engine. I run a bigger than stock battery in the area behind where the pass seat woul be.
lol! my brother had a 63 mercedes, and it would run for a week without the alternator (well generator)
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Old 07-21-11, 08:18 AM
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Originally Posted by jgrewe View Post
How long are your races? A carbed car can run for a while without an alternator. I used a stock idler pulley from the AC belt adjuster and got rid of 11lbs on top of the engine. I run a bigger than stock battery in the area behind where the pass seat woul be.
Its SCCA rallycross, I make 6-7 runs per heat (2-3 heats per event) around 1 to 2 minute runs then a few minutes of idling inbetween runs.

but its still plated and I drive it on the streets from time to time.

I use the alternator for these bad boys:

for the night events...

or frozen lakes
its like a scale model of a stage car, may become a stage rally car in 5-10 years (realistically)
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Old 07-22-11, 12:34 AM
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Oooooo, nice lights. I bet people think they are being followed by a baseball stadium with that many lumens in the air.

Keep the alt. lol
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Old 07-26-11, 02:28 PM
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they pull 8amps... each
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Old 07-26-11, 05:04 PM
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We ran some Cibie flame throwers on the front of a Datsun 210 for a 24hr race at Nelsons Ledges back in about '93. One of the guys had stuff laying around from his rally days. We had drivers come up to us and say they liked to follow us into corners because they could actually see where they were going and then they hated to pass us. Sucked for them, it was probably the slowest car on the track (ITC)
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Old 12-26-11, 12:52 PM
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i have a 87 gxl with a new battery and new alternator. its not holding a charge. at idle it stays below 12 volts around 10 11. and it drops a lot if i put a load on the battery
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Old 09-25-12, 08:36 PM
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Thanks, this helped out a lot!!!
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Old 11-26-12, 04:57 PM
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do any of you guys know were under the dash it would hook up to i want my dummy lights to turn off
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Old 02-04-13, 04:57 PM
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I have noticed with L terminal open I have been having voltage regulator issues, (read prematurely fail) thank god I got one with a 3 year warranty. This is mostly my theory right now but it does want to see a resistance for a charge light or voltmeter, so I just wired that terminal to an LED light I got from autozone. It is my everything is okay light, if the light is on - everything is not okay.
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