battery drain

[dmjlambert]

Multimeters have a DC amps function. Wire one into the circuit between the negative post of the battery and the negative battery terminal. You can wrap several turns of bare wire around the battery post, twist the ends, and use an alligator clip to connect to the negative multimeter lead. Set the multimeter to 10A DC range first. Connect the positive multimeter lead to the disconnected battery terminal. The current the truck draws will all go through the multimeter. You can run stuff that draws up to 10A, so don't turn on fans, horn, headlights, high power radio, starter motor, or stuff like that while using the multimeter.

Use the 10A function first, and plug the positive test lead into the 10A socket on the multimeter. If you switch the key to the on position and have the radio and other accessories off, you may find a couple of amps of draw from things like the distributor. Parking lights will draw another couple of amps. If you measure less than 0.25A with everything off, then you can plug the positive test lead into the volt/ohm/mA socket on the multimeter and switch the range to 250mA. Or you can just leave it connected in 10A mode. 0.1A = 100mA. If you read more than a couple dozen mA with everything off (and the key off), start unplugging fuses until you find the culprit.