Sometimes when my car is cold and I turn on the lights right after cranking the motor my volts will wave at me for a little bit. I mean it will drop from 14.4v down to 8v if I add another drain like brake lights it goes back up and if I let off the brake lights it goes back down and I can actually make the voltmeter wave back and forth like this for about a minute till it evens back out at about 14 volts. It's done this with 3 different alternators and I know it's not just the gauge as the lights dim when it goes to low voltage. It seems to be dropping back and forth between 14.4 and 13.6 volts at all times when I tested output at the alternator. I also have the same voltage problem after a high RPM run 5500rpm after motor has warmed up and can do the same thing with the brake lights I described before. It seems to bounce between 14.4 and 13.6 at all times though, warm, cold, whatever.

What's up?

 

Did I not explain the problem clearly enough or does no-one have a clue?

 

sounds like a loose ground some where....maybe taillights or in the engine compartment.........its like flicking a switch on and off really fast or sometimes when you barely put the switch in the middle but not all the way either the bulb pops or the switch shorts out. Maybe check grounds under your dash. also high power stereos with amps can kill alternators quick. I bought my car dirt cheap cause the p/o felt he had electrical prob. was really his sick stereo syst. he pulled it all out when i bought it and cured the prob for me.check grounds............my .

 

Hrm, if I had a bad ground, wouldn't it be bad all the time and not at more defined instances? No sick stereo here either, nothing even installed just a big hole in the dash where the head unit should be.

Happen to know where the brake lights ground at?

 

honestly not without my tech manual......if i find out after work ill let you know dude. As for loose grounds they work sometimes and then not. As for myself there are these connectors by my batt. that seem to have an affect on voltage readings........after a little driving for a week i lose a volt, tighten them ang it goes back to 13.5 with fans constant. once went down to 10 volts (scary) but tightened em and never below 12.9 hot w/ lights and signals.

 

yeah, mine will drop to 7-8volts when it spazzes out like this.

 

My thought is that the brake lights are fine and supplying a good circuit when engaged. I'd be looking at the headlight wiring. Possibly the dimmer in the switch itself.

 

I wish I could peg it down to one thing, but I was just using turning the lights on as an example. For instance, after a high rpm run, in the middle of the day at operating temps I will get the same voltage drop, and can get the voltage to wave back and forth between about 8volts up to 11-12 volts by say, turning the fan off and on, or by using the brake pedal to make the brake lights come on. It doesn't seem to be in any particular part of my wiring.

 

so what you are saying no matter what you use you get the volt problem

first thing i would try is got to auto zone and get the alt. tested (if that is what you are saying that is what i would do)

 

Autozone passes current alt, and past 3 alternators, unless I can get it into it's mode with a good long rev in the parking lot and fiddle with anything electrical to get it to drop the volts (headlights, brakelights, turn signal, etc). Then they just tell me what I allready know, it's putting out like 8volts. They've tested it on the car, and stand alone on their test bench, passed test bench too.

I should also mention, that previous 2 alternators both had same problem, I thought it was b/c they was reman. units, current one is brand new and still having same issue.

 

havin simular issues with my 90.The rpms drop off ahen it happens like my tach is pegged(haven't gotten around to the fix in this forum yet)And it actually goes from off the scale down to around 7000 rpm so that tells me theres a severe drop in current somewhere.New batt and advance/autozone/orileys all say alt has 103-105 output .Beginin ta wonder if i shoulda stayed pre 80 olds.At least those i know.

 

Yea my 1989 camaro deos the same thang i be getting like 8volts and stuff like that but when i just have my stereo on i get about 12 to 13 but when u turn my lights on and heater then it drops to 8 volts...
But i thank i may need a new battery cuz i thank the battery been in the car for about 6 years my buddy who i got the car from said dat is about the only thang i need to replace cuz he had to charge it up a few times. So i think i may be da battery on my end...

 

It has to be a bad connection somewhere between the starter and the ignition switch. Check battery and engine grounds also. When the voltage drop occurs you can use the opportunity to check for hot-spots. Both the battery and the alt would need to be bad if this effect is to be had from them so that's unlikely, whereas the guage and the loads all get their current from inside the car making the main supply wire the main suspect.

 

When I get the drop it drops everywhere, including the output of the alternator.

 

So you have measured around with a DVM and not just the factory guage in the dash? 8V at the alt would mean 8V at the battery, if the wiring is intact.. That would imply 2 things: the alt quit charging, and the battery is shot or there's a bad connection in between. Otherwise something would glow red..
The alternative: ground is not ground everywhere. Try to measure ground drops, bat neg to frame, to engine, and to alt casing. Also try to measure drop in the hot wiring, bat pos to gen pos, and to ign. Between bat, engine, and gen there should be no more than 0.1V drop anywhere. Have you checked the activation wiring voltage for the gen?