Alternator or Battery or something else?


Hello dear folks!

Brief question about my Mercury Trace Wagon 1977. Yesterday as I was getting closer to drop off a package at the fedex location, I heard the radio going dimmer and dimmer, so did the dashboard lights. After that, when I wanted to leave, the car of course would not charge.

I got it jumpered after say 10 minutes, started ok, got home safe, but then the same story. Got it jumpered again, read the voltage across the battery while idling: 6.5v.


The battery sort of recovered itself after the car stopped and went back to aprox 9.7v. So I am not suspecting the battery since I replaced it in October last year.

The battery is recharging now, and I am planning to go at Murray’s for a alternator testing - they have an in-store tester that they can test it with.

All odds are on the alternator, but before replacing that one I wanted to hear your precious advice and suggestions.

Thanks a ton!



It sounds like the alternator to me. I wouldn’t rule out the battery without having it tested.


I would have the charging system checked as well as the battery.


Sounds like the alternator to me too. Funny thing about batteries…mine never seem to give me any warning. Starts ok one day…dead the next time I try to start it.

If I have my theory correct: The battery is basically used to start the car, but it is the alternator that run the accessories and electrical system. While doing this, it also recharges the battery.

Anyone more knowledgable, please elaborate or correct me if I’m off base.


You’re close.

The battery supplies 12V to everything, PROVIDING the alternator and system is working properly and is keeping the battery charged.

The starter, upon initial use, uses the most power from the battery.