Can anyone possibly help me with a battery drain problem, I have a 93 F150 Lightning 5.8L 351W, for some strange reason when I let this truck sit for a couple of days the battery drains very low, the original owner had installed an aftermarket stereo amp, I took the fuse out, no progress, changed the battery because the old one had a bad cell, still no progress. Any help or ideas would be greatly appreciated. Thanks to all in advance: John

 

Could be a bad battery cable.. My dads was doing the same thing and it was a bad negative cable I believe. Other than that.. I can't really think of anything else.. Sorry I can't be of more help

 

To start with have the state of your charge system tested at a shop. Autozone is OK but a real shop will do a better test with a better machine. Check and clean all your cables and connections. Make sure they are tight not frayed. Once everything looks good and the battery is fully charged test for a parasitic drain. Turn off everything electrical. If you have a clamp on amp meter that's the best tool to use but you can use a cheap multi meter as well. With the clamp on just clamp it on to the battery cable. With a meter disconnect the battery and hook the test leads up between the battery post and the positive cable. If you see more than 1 amp draw something is wrong. Pull the fuses one at a time until the current draw stops. The circuit that stops it is your drain. I would start with the stereo system and any other aftermarket pieces.

 

Warlokk is right on the way to test for a shorted circuit.

You can also use a test light between the negative post and cable if there is a power drain the light will light up then as he said start unhooking things and pulling fuses till you find which circuit is causing it.

Also be sure to unplug and take the wires off the alternator to check it as I have seen quite a few of them cause a battery drain problem due to a bad regulator.

And I had an 80 that had a bad connection in the harness where the wires came off the postive post of the battery I like to have never found it.

 

Thanks guys for your ideas and suggestions, I will try them all my next day off. Mr. Smith, I noticed that the neg battery cable was taped like someone just replaced about 4" of the cable, I will replace the cable then try all the possibilities that were mentioned. Again thanks to all.

 

Just a note on the test light trick. It works fine on our trucks but done try it on newer cars. It is possible for a test light to damage the computer systems on modern cars and often you have no idea what is connected to a computer. Techs in dealerships generally don't even have lights anymore but a logic probe instead. But again it will work fine on our trucks.