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Resolved High Voltage from Alternator Problem

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TSiAWD666

Supporting Vendor
2,648
899
Aug 15, 2003
Herndon, Virginia
Hey folks,

Embarassed to say I'm having a weird problem with my alternator on my racecar. Right now it's outputting around 15.3V just after startup. Alternator warning light is on. I assumed my alternator's voltage regulator was on its way out so I replaced it with a remanufactured spare I had on hand, and I'm still getting the exact voltage and the light. I'm stumped, and I have a race I'm leaving for in a few days so I could use some help.

Some history: the car's alternator was outputting a typical 13.7V last year when racing. I had a tire explode that took out the wiring harness in the front driver's corner, and also ripped the male harnesses out of the corresponding female connections just where that harness enters the car in front of the driver's door. I splice in the whole section from the damage in the front corner, near the ABS, from a donor harness. The car in general is functioning from what I can tell as it starts up and runs. I'm not sure what to make of the higher voltage and alternator dash light.

Possibly related, my brake light stays on as well even though I have fluid in the reservoir, the sensor hooked up, and the parking brake off (the sensor work). Also, at the moment I have no dash lights which I haven't worked through yet beyond checking fuses, though I don't believe this would be related either.

I'm really in a time crunch, ideally I get this figured out by tomorrow night as I need to get the car out for an alignment before heading out to the track. If you're wondering why my dumb ass is trying to solve this now, that's a whole damned snowball clusterfck of another story :)

Thanks in advance, I'm really confused at this problem.
 
I'll give the battery idea a shot tomorrow. I do have a spare here.

It's a continuous 15.3v.
 
There's a thread on it somewhere on here I referenced when rewiring my chassis, but the brake light and the battery warning light are tied in together. Having trouble finding it now but might be something to look into with your wiring, since the brake light is on also with both alternators.
Reason I ask about the continuous 15.3v is mine shoots up almost that high for a split second after first firing up before leveling out. It's done this since I have disconnected the generator g terminal to leave it floating. It does not do this when the g terminal is connected to the ECU.
 
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May we assume the spliced-in harness was from the same year and model? Color codes change between Eclipse, Talon, and Laser, engine sizes, factory options, and years.

In other words, the red wire may not get connected to the other red wire. The fact that your brake warning light is on tells me there are more issues to be sorted.

It could well be a lack of ground issue, which would cause the alternator to "push" harder through distant, high-resistance ground paths.

In terms of resolving this before the race, maybe there is an aftermarket voltage regulator you can install to maintain the correct voltage until you can trace out the wire connection issues.
 
There's a thread on it somewhere on here I referenced when rewiring my chassis, but the brake light and the battery warning light are tied in together. Having trouble finding it now but might be something to look into with your wiring, since the brake light is on also with both alternators.
Reason I ask about the continuous 15.3v is mine shoots up almost that high for a split second after first firing up before leveling out. It's done this since I have disconnected the generator g terminal to leave it floating. It does not do this when the g terminal is connected to the ECU.

No kidding. Thanks for that tidbit! I never would have guessed they were electrically related.

May we assume the spliced-in harness was from the same year and model? Color codes change between Eclipse, Talon, and Laser, engine sizes, factory options, and years.

In other words, the red wire may not get connected to the other red wire. The fact that your brake warning light is on tells me there are more issues to be sorted.

It could well be a lack of ground issue, which would cause the alternator to "push" harder through distant, high-resistance ground paths.

In terms of resolving this before the race, maybe there is an aftermarket voltage regulator you can install to maintain the correct voltage until you can trace out the wire connection issues.

I was told the harness came from the exact same year and model, a 99 GSX with ABS (I think they all had ABS). The 99 was unique in the location of the ABS ECU I believe and the new harness had everything in place matching my old one. So I'm hoping/assuming it's the right harness. That leaves me with goofing up the splicing. I went over it a few times, especially since the first splice had me mixing some blue w/black wires up where one set was supposed to go ground and the other I don't know, and after that fix I double checked the connections and they all looked right and one to one. So I'm assuming that's right while I rule out other stuff at the moment, but... ugh I may be ripping apart that insulation again to look again.

On the ground idea, nothing had changed for grounding locations relative to the alternator. It grounds through its physical touching of the engine block, right? I'll look elsewhere, maybe I ripped something off.

Hmm, didn't think of an aftermarket voltage regulator. I'll keep that in mind as I troubleshoot more today.

Thank you for the ideas and info guys, really really appreciate it. If anyone else has more thoughts do share!
 
I FIXED IT!

Last night while googling I ran across this tidbit on alternator wiring on the ecmlink/dsmlink wiki (http://www.dsmlink.com/wiki/ecualternatorcontrol):
There are four wires running to the alternator. Two wires are G and FR from the ECU. The other two are a voltage sense line (from the headlight circuit) and an “S” terminal tied into the gauges somehow.

I bolded for emphasis. Headlight circuit? So I left out one apparently very key thing as I thought it wasn't relevant. While the car was down I was...bored and thought I would remove all relays and fuses that weren't in use anymore. So I pulled the headlight fuse amongst others, and a bunch of relays, out of the engine bay fusebox. After reading the aformentioned text last night I had a hunch me pulling the fuse meant I had disconnected the voltage sensing line for the alternator and that would explain why it was putting out its max voltage. I was skeptical though and really didn't think that could be it because I found nothing mentioning this in any forum posts, dsm or otherwise, but figured I'd throw everything back into the fusebox and see... and IT WORKED! Man, how the hell would anyone know they're related? Of course I say that and someone will read this and respond "DUH it's right in your owner's manual!" I've owned a DSM for 19 years and I had no idea :) What's also cool is this fixed my interior gauge lights problem too that I had no idea was tied to those lines.

Thanks everyone for the help. I doubt this knowledge will be of much use for anyone other than those who have race cars and/or re-wire the cars with non-OEM wiring harnesses, but maybe it'll be of use.
 
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Maybe the device that you are using to measure the voltage is not accurate?

Definitely a good idea. I tried two other devices, my handheld multimeter, and my RaceCapture Pro datalogger, and they were all showing the high voltage. Certainly something everyone needs to remember, sometimes devices aren't accurate.
 
Strange. Have you taken the old alternator to one of the box stores to have it tested? see if they can spin it up and get the same high voltage from it and we can then eliminate the car or the alternator from the equation.
 
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