[cbjohnson9]

Hey guys,

I'm sure there are tons of threads about this but my voltage light is driving me crazy. I've replaced my alternator and my battery...and my voltage light still comes on intermittently. No correlation with engine rpm, hot, cold, or anything really for that matter. It never comes on during initial startup either. I've had the new battery and alternator tested and they both passed. I'm getting about 13.5-14.0 volts on my voltmeter with the car running and all accessories on. When the low voltage light comes on, I'm still getting the same reading on my volt meter.

What else could be going on?

[stal94gt]

its not related to rpm at all, i know the belt routing is not the best for the alternator. on my car when i would give it alot of gas my battery light would pop due to a bad tensoner and belt slip

[cbjohnson9]

I replaced my tensioner about 10,000 miles ago

would the fact that I have a procharger be a problem?

The light will randomly come on even when i'm just at idle or cruising at a constant speed on the highway.

Is there some sort of fuse or relay that could be going bad, causing the light to come on?

[ZenMGT]

I'm having the same issue as you - at least I was yesterday.

My car was dead last week - so I went ahead and slapped in a new battery and alterntor.

One week later, I'm getting the battery light when the car is cold. I check the voltage and when cold she's about 14.3+V at the battery, and then drops to about 13.5-13.8 once fully warmed.

Two nights ago I put a brand new belt on the car to see if it fixed it. Next morning the light was on again

This morning no light

I also watched the voltage on my tuner, and while the tuner read about .5V lower than it really was it was consistent.


---I'm starting to wonder if that 'battery light' might also get tripped when the voltage is too high???

I checked my voltage everyday for the past few days and it's always good. The little indicator on the dash has been on the high side too (the needle just covering the right side of the battery picture). I experience no dimming of lights, and no other CEL's to speak of.

...so I wonder if the my new alty is just kicking out a tad bit TOO MUCH voltage when cold?

[cbjohnson9]

My car did die before I replaced the alternator. I've have no actual voltage issues since I replaced the alternator. Starts fine, runs fine...I'm just extremely reluctant to mash the gas with a possible voltage problem.

The light coming on for me is just so inconsistent.

If anyone knows what else might contribute to the low voltage light coming on please chime in here!!!

[ZenMGT]

I will say that since it's happened I've seen the light 'flicker' like there was a short arcing somewhere, and stay on solid for about 5mins.

I'd love to see the electrical schematic for the low voltage light. I thought I read somewhere it's not thrown by the computer, but by some simple little circuit somewhere. Anyone got that?

[bigjohnstud4200]

I had the same problem and my two separate auto parts places told me the battery and the alternator tested good. I would run live data logging while driving and the voltage would be fairly constant and I could see no drops when the light would come on. I read somewhere that the voltage regulator could still be the problem with spikes etc etc etc. I replaced the battery first since it appeared to be original and the problem went away for a couple weeks then i started again. I then replaced the alternator and it's been a month with no problems. I found a new motorcraft 160 amp alternator for $85.00 on ebay and got it in like 3 days with standard shipping. Let me know if you want the seller details.

good luck.

[cbjohnson9]

I've noticed that flickering problem also. It's like the alternator isn't kicking on right. It sounds like the alternator is bad despite the fact that it's less than a month old.

Bigjohn did that alternator come with a warranty?

[ZenMGT]

well my light came on again this morning, only for a minute, then out.

Look at my diablo I was putting out over 14.2 - which from what I've seen is much lower then the actual voltage, so it was probably putting out closer to 14.5+VDC.

I'm wondering if MY light problem is too high a voltage - vs the more common too low voltage. When my light went out the diablo was saying about 13.9VDC.

[cbjohnson9]

Before this new alternator, I was running a 160amp with no voltage problems at all...until it went bad. The one I threw on this time is a 130amp. I was thinking too much voltage might have caused the voltage regulator to go out sooner than normal (the 160amp alternator only last about 3 years). Do anyone have any comments regarding alternator replacement and if you should get one with more amperage vs. replacing it with just a stock piece?

[PhxMustang]

It is possible the altenator you picked up is afaulty. I went through three of them in 2 months. Ghetto referbs from autozone finaly got a good one. Also check the connector cap on top of the altentor. If lose or worn you will get the light. I recomned some contact grease.

[bigjohnstud4200]

Originally Posted by cbjohnson9 Bigjohn did that alternator come with a warranty?

Mine came with a one year through the seller (a shop).

Originally Posted by cbjohnson9 Before this new alternator, I was running a 160amp with no voltage problems at all...until it went bad. The one I threw on this time is a 130amp. I was thinking too much voltage might have caused the voltage regulator to go out sooner than normal (the 160amp alternator only last about 3 years). Do anyone have any comments regarding alternator replacement and if you should get one with more amperage vs. replacing it with just a stock piece?

The alternator I purchased is a Motorcraft 160 amp (at least that's how it was described to me). So far, it's been over a month and I haven't seen a flicker yet.

[00jerm]

I had the same issue with my 04 gt. Its got a vortech on it and I went thru 3 alternator rebuilds in two months. Heres the deal. I called PA Performance and told them about what was going on and they said I was overspinning my alternator shaft. With stock balancer and alternator pulley and my redline set at 6300 rpm I was spinning my alternator shaft over 24000 rpm. Its only rated for 16000 rpm (most all are set for this, retarded I know) so I bought a new 130 amp alt with a bigger pulley that when I'm at redline will spin the alt just under 16000 rpm. Car is sitting at around 14.4 volts now and drops slightly to 13.6 at redline like its supposed to. It will be lower volts when hot and more volts upon initial start up. I also got an AEM digital voltmeter and mounted that bitch right in front of my face on a column gauge pod so I can seed if bad news is heading my way! Hope this helps.

[ZenMGT]

...well to update. I haven't done anything (replace the alty yet), and the light still shows up only once every morning. Stays on for about 1min., then never comes back during the day. Like something is out of whack when cold.

I believe I'm putting out too much juice when cold. When I get some time I'll slap an O-scope across it, and see how noisy things are. My car runs great otherwise....

[cbjohnson9]

Originally Posted by 00jerm I had the same issue with my 04 gt. Its got a vortech on it and I went thru 3 alternator rebuilds in two months. Heres the deal. I called PA Performance and told them about what was going on and they said I was overspinning my alternator shaft. With stock balancer and alternator pulley and my redline set at 6300 rpm I was spinning my alternator shaft over 24000 rpm. Its only rated for 16000 rpm (most all are set for this, retarded I know) so I bought a new 130 amp alt with a bigger pulley that when I'm at redline will spin the alt just under 16000 rpm. Car is sitting at around 14.4 volts now and drops slightly to 13.6 at redline like its supposed to. It will be lower volts when hot and more volts upon initial start up. I also got an AEM digital voltmeter and mounted that bitch right in front of my face on a column gauge pod so I can seed if bad news is heading my way! Hope this helps.

the centi blower shouldn't affect the alternator speed unless it causes slippage due to the belt routing. If anything it should decrease slippage on the alternator because the belt wraps around the alt pulley more now. I have the stock pulleys on the car, but it would be extremely stupid for the alternators to have an rpm limit set below what the alternator speeds can reach stock from the dealer. I'm thinking faulty alternator. I'm gonna have a few different places test out my setup and see if it passes or not.

[00jerm]

I couldn't agree more cbj9, why ford made garbage alternators I don't know but my new one works great and has that bigger pulley on it. my car had the same alt issues before being supercharged. When it was stock.

[cbjohnson9]

where did you get the bigger pulley for it?

[cbjohnson9]

Update...
New battery, new alternator, new tensioner, checked all the grounds...and the light still comes on randomly.

my lights flicker once in my car, then my voltage light comes on. sometimes it stays on for a good amount of time, sometimes it goes off in a few seconds.

The guy at NAPA talked to his rep about alternators and he mentioned that the voltage regulation programming on our cars gets messed up and causes the alternator to not function correclty. Has anyone ever heard of this?

Addtionally, is there any external voltage regulator on our cars that could not be functioning correclty. Could a fuse or relay be bad?

Voltage read out with and without the light on is the same according to my volt meter.

[bigjohnstud4200]

Originally Posted by cbjohnson9 The guy at NAPA talked to his rep about alternators and he mentioned that the voltage regulation programming on our cars gets messed up and causes the alternator to not function correclty. Has anyone ever heard of this?

I've never heard this before, but I wondered the same thing when I had the problem. I tried removing and reinstalling my stock tune and it continued to do it. New alternator was the fix for me. Have you checked the wires to/from the alternator?