Hey, I have a bit of a problem...Lately my '79 has been acting up. I will start the car and the voltage will read around 13 volts...But as I am driving, my voltage will decrease until the car doesn't have enough power to run (around 8 or 9 volts) and dies. This is especially true when I try to drive at night with the headlights on...I don't seem to get more than like 1/2 mile before the car dies. Is the car running off the battery to make up for the alternator's lack of output or what? what the heck is going on?

 

Sounds like the alternator may be bad or it could be the battery has gone bad and won't hold a charge. Check the water level in the battery. If it is good take it to a parts store and have them check it. Most will do it for free. You can also take your alternator and they should check it for free also.

 

It has got to be the alternator. Even if your battery is no good or disconnected, once the car has been started it should read 14v the whole time. With accessories on at night, and the engine at idle the voltometer may drop down a little to 13v but that is normal.

I would assume that once your battery voltage drops down to 8v and the engine dies then you can not start the car.

 

Yeah, every time i ran out of juice and the car died i had to get a jump from somebody to get going again. I just had the alternator replaced last summer and the battery replaced like 6 months ago. And I had both of them checked out last week at like auto zone and they were fine. Of course, I was only having minor voltage drop problems...They're much more drastic now...So I'm still not sure what to do. I have had problems with too much slack/slipping in the alternator belt but I mean now I have the alternator slid as far out on the mounting bracket as it will go...

 

make sure the belt is tight. Than can cause a slight loss in voltage output from the alternator. The only other thing I could think of is that maybe your battery cables are ready bad or you are running upgraded headlights/fog/running lights and a really high amperage sound system while all this is going on... is that the case?

Also, those rebuilt alternators at parts stores sometimes only last a year or less. Same goes for their rebuilt starters. Buy the lifetime warrantee ones and save your receipt.