I have a 1970 Mustang coupe, and I think there may be an electrical issue. I just bought a 100 dollar battery last week, and it's already dead? It cranked fine yesterday but today it won't start, and it's obvious it's the battery by the sounds. The Cig lighter is plugged in, lights are off, electric heater was turned off, windshield wipers were off as well.

Any thoughts?

Check your charging system, if not the prob then check for draw

Charging system such as the alternator?

Bad alt or not, a brand new battery would not just quit over night, unless you drove for a few hours and the car ran off te battery with no alt charging it.

Something drained power. Goodluck, these gremlin can be a MASSIVE PITA

But this is rule of thumb

If you hve a aftermarket stereo/subs. Go there first
If not, think back. Did anything electric related, not work, act up, not do what its supppse to etc etc

grab your volt meter and go to town bub.
First thing I'd check is the alternator, then the leads to the alternator, and so on. If the wire going from the alt to the battery is shot, that could be the issue. I've had that happen on an old ranger, it would pop when it started. But it didn't "look" bad. I was young then lol

at this time of year that is completely untrue. the cold weather is hard on batteries, and if the alt is not charging or barely keeping a charge on the battery, it will go stone cold dead over night.

location is relevant of course.

This post was edited by Sonicgundam on Nov 27 2013 05:00am

What im sayin is, the only waythat battery is dead if this guy drove his 1970 mustang in this weather witn a bad alt, and it was not charging the battery as he was driving, and the radio etc was running off battery power alone. Or theres a short/somethig drawing power when its off.

Which i would assume is what he did. Put the batt jn, start it up. Park it, and thats all. And there is no way that kill this batt.

In which case you could chew my fingers off before you could make me drive my 1970 mustang jn this weather.

Chances are this brand new batt didnt just freeze cock solid for no reason

This post was edited by IB0T on Nov 27 2013 07:26am

If it's the stock charging system, the alternator uses an external voltage regulator, which from your symptoms makes me believe this is probably the weak link. If the regulator is defective (considering it's age, this doesn't come as a surprise) typically they draw back from the battery, regardless of key/ignition position.

But before you do anything, if you haven't already, grab a multimeter. Also, put a fresh charge on the battery. Once the battery is charged, start the car. Check the voltage of the battery at an idle, and revving. Note any fluctuations. Voltage "should" be around 14 volts with the car running. Don't trust the ammeter in the car. Use a multmeter.

Again, this is assuming everything is stock, all bets are off if things have been touched.

This post was edited by OldAndyAndTheSea on Nov 27 2013 08:22am

I'm pretty sure you hit it on the head with the voltage regulator.