HOW TO FIND A BATTERY DRAW
1.) Get yourself a multi-meter ( make sure the fuse inside is not blown and the leads are in the correct posts to test for amps) and disconnect the positive terminal on your battery.
2.) Switch your multi-meter to amps and attach the positive lead from the multi-meter to the positive terminal on your battery and the negative lead from your multi-meter to the positive cable on your truck, make sure no lights are on ( don't forget the hood light, remove it if you have to ) in the truck and the keys are in your pocket and walk away for about ten minutes, this will give the ECM and any other components time to completely power down.
3.) After ten minutes look at the multi-meter, this will be your draw in amps ( voltage is not as important than amps when it comes to battery draw). this number SHOULD NOT BE ZERO so don't worry if there is a small amount of amperage being drawn. you have a lot of custom settings the ECM has to remember.
4.) start pulling fuses under the hood keeping an eye on the multi-meter, if any fuse is pulled and the multi-meter value changes you have found your circuit with the issue, at this point consult a wiring schematic to trace the wires and inspect them for breaks.
.5) if no fuses on the exterior fuse panel show a draw then open the drivers side door. After opening the door you should have a large draw on your multi-meter due to all the lights coming on, write this number down because you will need to subtract this number against the original one to isolate the circuit in question ( I.E if you have a base draw of 2 amps and with the doors open you have a 5 amp draw that means you are looking for a 2 amp difference when fuses are being pulled. *extra note- one of the fuses being pulled will turn off your lights so in that circumstance the amp should go back to the original value UNLESS the courtesy light circuit is the issue ). After you have the normal draw and the door open draw written down start pulling the fuses inside to see if any of those circuits are the issue, if you see the number (draw) drop after you pull a fuse ( NOT the courtesy light fuse unless the amp draw drops to almost nothing ), then you have found the circuit with the issue and again, consult a wiring schematic to trace the wires and inspect them for issues.
6.) If NO fuses showed any difference in your draw then there are still a few other components that may be causing your issue. first disconnect your alternator from the truck, if no change in draw then disconnect your starter, if still no change then unplug your ECM and check the draw.
7.) If you have done all of this and you still have a large draw then you either have a after-market piece of equipment hooked up to your batteries that is bad or you have a very tough little gremlin that I would take to a shop.
in my experience 90% of battery draw issues come down to after-market additions I.E. Amp, CB's, HID lights, Alarms, etc. A good move would be to disconnect all after market items first from you battery to make sure its not one of those before proceeding.
For me, I actually ended up wiring in a switch for all the courtesy lights so I could turn them off. they seem to draw ALOT of power when on so i just removed the fuse on the interior panel and replaced it with a fuseable link to a toggle switch.
