Unknown battery drain

[Jim Brizz]

Hello, I'm new to the site and this is my first post. I have a 1992 F-150, manual shift with the straight six. I don't drive the truck every day, and recently I tried to start it and the battery was stone cold dead. I charged it up, and a day later the battery had no juice again. I bought a new battery, since the old one was eight years old. When I went to work today I noticed that the amp light on the dash was on when I turned off the truck. Just four hours later, the new battery was almost dead, and I had to jump-start the truck. Does anyone have an idea where I should start to look for what's drawing amps when the car is parked? Any help would be appreciated; I have to use the old girl next week for duck hunting.

 

[5.0Flareside]

Check the alternator first and foremost.

 

[Jim Brizz]

Could something wrong with the alternator cause a draw on the battery when the truck wasn't running?

 

[john112deere]

I think what Chris is getting at is that the alternator might not be recharging the battery while you're running, or not recharging it well enough to start.

I'd start by putting a voltmeter across the battery while it's idling- I'm having a brain cramp and can't remember exactly what voltage you should be seeing, but it's well over 12 if all is functioning correctly. (13.5+ at idle, maybe?)

I guess a real simple alternate test would be to unhook the battery and leave it overnight, see if it'll start the next morning. If it starts good, something's draining your battery while parked- if it's dead, you're not recharging properly.

I'm assuming you've already looked for the real obvious stuff- brake lights aren't staying on when you leave it, dome light shuts off when you close the door...all that kinda stuff.

 

[BuzzGun79]

hookup the volt meter to the battery,while running it should read 13.8 volts. do you get a spark when disconnecting or connecting the ground? if so something is drawing it down. if you have an external mount voltage regulator an open circuit will also drain the battery.if its more than 2-3 yrs old replace it they are not costly & cheap insurance.a poor or loose alt belt will not charge properly.check all inside dash & underhood courtesy lights to see if they go out when closing doors & hood.

 

[Jim Brizz]

I left the battery dis-connected overnight, and the truck started right up. While it was running I put a meter on the battery, and the alternator was putting out 14.2 amps. When I turned off the truck and removed the key, that amp light was still lit up on the dash. I checked lights such as the glove box light that could be staying on, and found nothing. I think something's drawing power when the truck is just sitting still.

 

[73F100Shortbed]

Well the amp light being lit up after key is out would drain the battery if it is on all the time.

 

[silverz51]

This might sound stupid, but you might want to check the battery cables. If they are corroded somewhere or the ground is not good, that could cause your battery to "appear" dead or even prevent it from charging properly...

Just saying...

 

[blacksnapon]

regulator is defective in the alternator.

 

[sgarver]

regulator is defective in the alternator.

Had the same thing on a 93. With the engine off and key out, the amp light stayed on. Put a good used alternator in it and the problem was solved. I didn't want to buy a new one without knowing for sure that was the problem.