Glow plug control modules have been known to “keep the lights on”. Unplug overnight and see I’d the issue goes away.

Your right Mark, not a GPCM code.

I’m not sure if his ‘04 has two IAT or the second is embedded with the MAF, when it is its 6 wire. History says it can be the wires too with the dual purpose MAF since they are usually handled poorly during removal.

When working electrical issues concerning a key off draw, I’ve figured out if you open the hood you can monitor the underhood light to determine when everything has gone to sleep. I’ve timed mine and it’s 10-25min. Not always the same amount of time, I would have though it was on a simple timer but apparently it’s more complicated than that. I’m confident though if the hood is up and the light has turned off, everything is asleep. Also voltage is a fair indicator of draw over time but amps are more accurate. There is a generic list of mA draw for many of the common modules and circuits that can be helpful if you know the draw value on your truck.

On most modern vehicles it’s hard to do a parasitic draw test because when you hook up the meter it completes the power circuit and some of the modules “wake up”. On our trucks it’s easier, attach the DMM on it’s highest scale (10 amp is ok, 20 is better) to one battery, in series. It will be accurate on the positive or negative side but the negative is safer. Once that circuit is established, unhook one of the posts of the other battery and read the meter. As I said above, if you interrupt power to the truck, even for a second, and reconnected it the underhood light will come on and you’ll have to let it go back to sleep and start over.

A voltmeter, or DMM is often discussed with parasitic draw problems, along with a whole series of diagnostic videos.

A voltmeter is one tool, measuring pressure to use that analogy. But while a voltmeter is is many people’s tool box, a simple but cheap clamp-on ammeter is not. And many times a clamp-on ammeter can be the best tool for hunting down parasitic draws. For me it’s an unmentioned $50 tool.

I realize electrics seem to be confusing to many, but the analogy of water or hydraulic plumbing, while most sparkies cringe, is a good way to think of the situation. A clamp-on meter placed on the 4ga cable from the drivers battery to the CJB would have told if the direction of flow was towards the cabin, alleviating pulling the dash apart or PCM harness. If it’s not the main 4ga to the CJB, the 4ga cable off the passenger battery would be checked next, as it connects to the alternator and the GPCM. With that cable, it splits to either of those components and can be traced.

If towards the dash, then it gets somewhat complicated due to the open door influence, but that may or may not be a factor. Pulling fuses, closing door, and rechecking amp flow to the drivers side 4ga can then be used to diagnose without pulling everything apart.

yeah