Always start with the simple stuff. Do your battery terminals look like chia pets? if so the corrosion can cause a huge increase in resistance, cause a whole bunch of issues. I had some on my truck, and my alternator had large amounts of voltage ripple, and my audio system sounded poor. I cleaned the terminals and applied the corrosion protectant and it was fixed. Make sure the alt. isn't failing to charge properly, look for around 14.0V area with no loads in park. Use a screwdriver and touch it to your ear then the alternator and listen for any bearing noise, it will sound like something is stuck in the garbage disposal if the bearing is bad. Have the truck idle for a good 30 or 45 mins, then feel the alt. If it smells hot or burns the living crap out of you the windings are bad, and can cause int. charging issues and parasitic draw issues. IF all that is good then disconnect the negative side of the terminal while leaving the positive connected and set your ports of the multimeter to the amp side, it will be fused at 10 amps. Do not use this mode for anything but amperage as it will blow that fuse. Make sure the key is out of the ignition, so the dinger is not going off and unplug the engine bay light. Open the driver side door and tape the door jam switch closed, you will need to be able to access the interior fuse panel and if that switch is open it will cause a increased reading in amps. Hook the positive side of the multi-meter to the disconnected negative terminal, and the negative side of the meter to the negative post of the battery. This will measure the amount of amps or drain on the battery that we can use to find the parasitic draw. Leave the multimeter hooked up at all times, and disruption of the current will not allow the PCM to go to "sleep". after 45mins, the PCM will stop using battery voltage to power itself and rely upon its internal capacitors for storage of memory. After this you can read how many amps the battery is pully. Any amount under .060 is good, or 600 milliamps. If its higher then that, then you have to go and pull each fuse and relay one at a time, and watching your amps to see if it drops. IF it doesn't drop reinstall it. IF the amps jump up again after reinstalling fuse then wait a good 10-15 mins to allow the PCM to return to sleep. Once the fuse is pulled that caused the amp. to drop we can isolate that circuit as having an issue, usually a short somewhere. Voltage is not an accurate way of testing for a draw. To simplify ohms law you can use alcohol as an example. V= how strong the liquor is. OHMS = Your natural tolerance to alcohol. AMP = How much you drink. WATTS= how drunk you get. You could drop from 13v to 11.5v, but if its only .050 amps, it wont drain the battery, much like having a shot of vodka. But if you barely see a drop in voltage, and your pulley 1.5 AMPS, we have a problem, like drinking a case of beer.
