91 chev p/up slow battery drain

[x1957x]

I have a buddy that has a Boat pulling Machine (91 chev p/up with a 350cu.) that if he charges A NEW BATTERY to full, it will discharge at about 2 weeks or so and be dead. Any way a person can test whats happening or where to look. Yes he does have the hookups on the back for the trailer lights. My thoughts were in that direction but not for sure where to start to look. Thanks 57

[gixxer01]

A multimeter will be needed. You start by determining the total amp draw at the battery. Set the multi meter to read amps and place one lead on the disconnected positive cable of the batteryand the the other on the the positive post of the battery. This will tell you the overall amp draw. Next step is the pain in the arse! You need to determine the amp draw for all circuits in the vehicle in much the same way. Pulling out a fuse and using the multi meter to complete the circuit is the easiest way to do it.

Are you sure the alternator is charging the battery?

[Jeremy airjer W]

Is the truck driven everyday?

This is the same as the above but maybe a little easier. Do this with all the doors closed, lights off, keys out of the ignition.

With the positive cable end removed from the battery place one lead of a voltmeter set to read amperage on the positive post of the battery and the other lead on the positive end of the cable. You should see less than .050 amps and more likely less that .020 amps. If you have more than .050 amps than leave the voltmeter connected the way it is and start pulling fuses one at a time. When the draw goes away focus on that circuit.

[delcecchi]

Does it have a light in the glove compartment or under the hood? Remove the bulb and see if that helps. (the systematic approach is more likely to work but this is really easy.)

[x1957x]

Jeremy. I went to my buddys house and looked at his truck today and i hooked the volt meter up on the positive post cable and battery to see what we had. At the battery it was a .1 drain until we pulled the brake light fuse and the gauges fuse and then it zero'd out on the tester.. What do you do next?

[Jeremy airjer W]

It shouldn't drop to zero so I would need to know what it dropped to when you pulled each fuse individually.

[Jeremy airjer W]

Is the fuse labeled "brake" or "stop". If it is "stop" than its in the lamp circuit. If it is "brake" than its in the rear ABS circuit.