My 1972 Cutlass Supreme has been pretty modified by the previous owner. It has an aftermarket sound system, MSD ignition, electric fuel pump and fan, and has been upgraded to a 130 amp system. If I let my car idle for about 2 weeks and try to start it, its like its dead. So I began troubleshooting what may cause this. Disclaimer - I don't really like messing with electric.

I thought maybe my Alternator was draining even when my car was off. I unplugged it and measured the voltage of my battery daily. It started off somewhere in the 12V and then lost a 1/10 of a volt a day it seemed. It also seemed to plateau around 11.5 Volts. Today when the battery was at that level, I tried to start it and the car wouldn't turn over (all other electric worked). I went ahead and plugged up a trickle charger for a short while and then tried to start my car. It started right up. I let the car idle for about 5 minutes and noticed my Volts of my battery were reading all around the 10-12 range. I shut off my car, tried to start it again and the starter wasn't getting enough juice to start the engine. My battery was reading about 10.6 V.

So my questions are:

1) Is there something wrong with my alternator?
2) Is there Something wrong with my battery?
3) What other test do you recommend?
4) Do you have any other ideas what might be wrong?

Thanks

 

Is it a one wire alternator or a newer GM version? If it is one wire you have to energize it to start charging by revving the engine up to maybe 1500-2k to get it to go into the charging mode. If it isn't a one wire then I'd be looking at the voltage regulator.
Many on here are much better at the electric side of things so they will chime in soon.

 

It is a one wire one. Good to know about that charging information.

 

also, if it's a cs-series alternator, if the system voltage isn't at ~ 12 volts minimum, it won't even try to charge.

put a real charger on the battery and re-measure the voltage after it's fully charged.


bill

 

You need to put an ammeter in series with the battery, see what it reads, then disconnect circuits one at a time until you find the drain.
Remember that any later electronic devices will each pull a small amount of current (probably about 100mA) for their memory.

- Eric

 

I had simular problems with a '69 - turned out to be the positive battery cable, [which looked fine] had internal corrosion.
New one fixed it forever!