ok so my dad backed into my bumper a few weeks ago. It jammed the left headlight motor and kept draining the battery, i finally fixed that by disconnecting that motor and put in a new battery and alternator. Youd think that would fix it ... thats the whole chargeing system ... but nooooo not this f*ckin car ! Somehow the chargeing system works when i first start the car for the day, usually lasts me all the way to work, and then home at the end of the day. But once i turn the lights on, or the rear defrost, or any combo of things that draw too much power the volts drop off to twelve, meaning the battery is now powering the car. Then it stays that way for the rest of the day. The alternator is fine, already tested it with the car running, pushes 15 volts when not connected to the battery, but once it is connected it drops to 12. Ive been trying to track the problem for days but for the life of me i cannot figure out what the hell is going on. My only guess is maybe there is either some type of relay in the front end that got damaged when my dad hit it, but i cant find anything and my repair manual shows nothing. Or there must be some type of one-way device that only lets the alternator charge the battery, and not let the battery power back to the alternator, and that is bad. I know the main power wire at the alternator is at 12 volts when the car is off but im not sure if thats normal or not. This is driving me up a wall and im seriously thinking of running the car into a lake or something to collect the insurance money ... anyone with any idea at all please help me out on this one. thanks.

btw the car is an 89 gtu model.

 

If the alternator has a warranty, get another one to rule it out. Cheap reman ones almost always have bad regulators. 15V sounds high, but a drop to 12V while running is definitely fishy (13-14V is ideal).

I had a problem like that (not caused by damage though), and I tested the current draw of everything I could think of, replaced my battery cables, etc...and it ended up being that my "new" alternator was a pos.

 

alot of the S4's have a tendency to Have Crappy grounds.They make the alternator Work "overtime" when the Lights,etc are Turned on..Now,you were running the battery Down alot Lately,and that could Take it's toll on the battery also..Have you checked the Wiring around the headlight area to make sure that there isn't any Bare/shorting wires?..Myself,I have never Seen my Car run at 14volts With the Headlights on.It Dips down to just over Twelve..and that is why I am Upgrading to an FD alternator..I'm sorry I can't help you more,If it was more of a Stock problem,I may be able to .But when you toss in a Crunched headlight motor,it gets Sticky!...I just have ONE Question though.: Has the car ever DIED on you,since the Alternator was replaced?.Will the Car run With Lights On,and the voltage at 12?..(and it the Voltage stays Constant at 12v.?)..If it Stays at 12 and Doesn't die,Honestly,I would Say OK..GOOD..but if it Sucks Juice from the battery with Lights ON and the Voltage Keeps Dropping,then I would Be Looking at Taking the Alternator Back(just Because "you can"),and try another Battery,First With the alternator you have ON the car,then with another Alternator..Good luck and post with any Results.STYX.

 

Well i did repair the bumper, the light is going up and down again, so thats back to normal. But the problem is still there. And this is the S5 model. Ive been looking for short circuits all over the car and i havnt found anything yet, especially around the headlight that got damaged. and about the charging system being at 12 volts for a while, i try to avoid that situation by not driving at night and causing the drop from the lights. I drive to work most days and it doesnt drop at all, not using lights or rear defrost just heat and radio it does just fine. If i take it out for a spin and see the voltage drop i drive it home as fast as i can so im not sure how long it would last like that, but the voltage never drops below 12. I just assumed that was because it was a new battery though. I drove the car about 30 mins away the first time this happened and by the time i got there voltage was at 8 volts and i could barely see the road cuz it was at night, but that was with the first alternator. As for the new alternator, when its working hooked up to the battery its putting out 14 volts, it was at 15 when i had it completly disconnected from the car to test it. I bought this one from a guy on here actually, it definetly charges so i know its good, which means my old one was probably fine also. The car has never died on me because of the alternator. Could someone please tell me more about the regulator, and if i could just replace that ?