'90 coupe voltage fluctuating
 

I have a 1990 coupe. When I have the headlights on and I step om the brakes, I notice the lights dim a little and the voltage drops a little. And then when I have the stereo on and I hit the brakes the voltage gauge needle flickers around but drops to what looks like 12 or 13 volts. One day last week my car was totally dead, then when I charged it up and started it the car has been doing this ever since. I put a brand new(not remanufactured) alternator on it and it is still doing the same thing. Can anybody tell me what's causing this? Thanks for any help anybody can give me!

RE: '90 coupe voltage fluctuating
 

I have a 96 vette and had that same kind of problem, but it was the battery that was bad. Not saying that is your problem...but that's what mine was. replaced the battery and it has run fine since. Good luck.

RE: '90 coupe voltage fluctuating
 

You need to have your battery load checked by someone compentent (not Autozone:)), sounds like either a weak cell in the battery or a poor connection.

RE: '90 coupe voltage fluctuating
 

Advance Auto Parts did a great job checking mine and they were right about a bad battery. Ifit is weak, they can charge it in a few minutes, then check it. It's free, too. Hope this is the problem, since it is the easiest to find and correct.

RE: '90 coupe voltage fluctuating
 

Hey berts...

Did you put a multimeter on the field terminal of the old alternator? What was the readin'?

RE: '90 coupe voltage fluctuating
 

Hey guys thanks for taking time to reply. I never tested the alternator, it was a lifetime warranty so they replaced it without checking it.With the old alternator on I did put a multimeter on the battery while the voltage was fluctuating and it was showing over 14 till I turned the lights, ac, and stereo on then it jumped wildly fom 14 down to 5 and everywhere in between. With the new alternator on i checked it and it's only dropping to 12.5 but when I put it in gear the needle drops probably to 10 or less. I need someone to put the meter on it then but I don't have anybody here. I think I will go have it load tested. Thanks for all the advice, I will report back when I find out something!!

RE: '90 coupe voltage fluctuating
 

Hey guys, I went to Advanced Auto Parts and they load tested the battery and said it was ok, and said the alternator was ok, but my car started loading up and I almost didn't make it home. Any ideas on what it could be?

RE: '90 coupe voltage fluctuating
 

Normal.

Still normal.

Test the field output while runnin'. Put the positive on the field stud on the back of the alt., and ground the (-) probe. Look for 13 - 16V.

Then check what's goin' to the battery. Multimeter (+) on the battery clamp screw (must be a corrosion-free connection (not over-torqued!)), (-) on the frame. Should be well over 12-13V; maybe a little more.

Then check what the battery's takin'. (+) on the positive clamp screw, (-) on the negative clamp screw (you have to make sure the (-) screw is absolutely corrosion-free into the battery (-) post).

Then check the battery ground cable. Multimeter (+) on the (-) clamp screw, (-) multimeter probe on the block/frame. Should be the VERY close if all is still well.

If you have only a no-start issue due to battery re-charging, you'll find the problem there.

If the no-start issue is due to a battery drain, we'll cross that road when the chicken shows up.

Post back what ya' get...