Dead Short

I only drive my truck about 200 miles per month. The battery goes dead in three days while sitting. I've had the charging system and battery load tested. It tests fine.

If I disconnect the negative terminal to test for current draw, it's pulling a solid 12 1/2 volts at all times between the disconnected terminal and the battery terminal.

The current draw started after I installed a new window motor and regulator in the passenger side. It still pulls current if the fuse is pulled and disconnect the switch to the window motor. So I think that a defective window motor with a short to ground can be ruled out.

Also, if I pull ALL of the fuses, including the 100 amp fuse to the alternator, it still draws a solid 12 volts.

In addition, if I disconnect the wire to the starter it's still pulling twelve volts.

Only if I disconnect the line to the entire fuse box does the current draw stop.

Since it's the only thing that is wired directly to the battery, I can only think that I have a bad ignition switch, and the switch is operating normally.

The only thing weird that I notice, is that when I reattach the negative cable to the battery terminal, the relay to the rear taillights clicks, but if the relay is pulled, it continues to draw current.

I'm confused and out of ideas. Does anyone have any thoughts they would like to share.

 

Yes. Through the 1st half of you post I was thinking, "Aww man, disconnect the + line from BATT to engine fuse/relay!" and then ... you did. That's supplying voltage to everything inside your cab and a few other key things. So we know whatever is causing the parasitic draw is downstream from that fuse/relay box specifically. That's where I'd start my process of elimination.

With truck off, setup your DMM to test for amp draw, even if it means zip-tying one lead to the - battery terminal, other to the terminal clamp so you don't need 4 hands.

Moving to the engine fuse/relay box, incrementally pull fuses and reinstall, one by one, watching for drop. Do you see anything?

There are some more-difficult to remove items in there. Start with the easy micro-blade stuff first, move to the relays, and I wouldn't touch the 100A+ alt unless nothing else pans out, but ... that's also a possibility, I suppose. But may be easier to test if alt is bad by popping off its power directly. That's not a definitive test though, could be a short in between.

 

Did exactly as you suggested. Held the DMM leads to the negative terminal with plastic clamps. Pulled every fuse, and I mean every fuse, including the 100 amp fuse and still had a parasitic draw. Weird.

 

And just to re-cap, if you have the DMM setup on the negative battery cable as you mention, and you remove the small piggy-back line between the positive clamp and hte engine fuse/relay block, the parasitic draw disappears?

If not, I'd be looking in the engine bay.

If so, the only other things I can think would be to look for something shorting out underneath the engine bay fuse/relay box, or an issue with the actual small piggy-back line between the battery clamp has a short in it. Like what? Check this out for one example, that's from a recent case we saw on here. Read the whole thread for fun.

 

There's a fuse box on the inside too, isn't there?

 

Definitely. But IIRC, in the EWD, power to that box is fed entirely through the engine bay relay/fuse box.

I think OP said the draw goes away when removing the wire that goes from the terminal clamp to the engine bay fuse/relay box.

If so, that suggests the issue is something that sends or receives power through that engine bay box. That could be (A) anything downstream inside the cab, much of which lies on the other side of the in-cab fuse box, or (B) something in the engine bay which routes its power through the engine bay box.

I can't recall how the alternator is wired, I'd assume it's Alt => Batt(+) => 140A relay = ??? but dunno. I recall the post I just linked where that OP's 140A fuse shorted and was causing issues with charging, which doesn't make sense to my feeble brain unless it's Alt => 140A relay => Batt+ => ???.

 

Just to clarify, you are testing for amperage draw and not voltage, correct? It will always have 12v when connected, it's a 12v system. You're looking for current draw in amps. should be below 0.05 amp draw with the vehicle off. As little as 0.13 amp draw was enough to drain my battery after a couple of days.

 

This is from the EWD for the 2000 model. I dunno what year OP is driving, though, not in their profile unfortunately. Anyway, the correct way to diagnose this would be to hit up the forum's EWD section, put their DMM on neg (-) side of the battery the circuit while set to test AMPERAGE (not voltage), then slowly work back. Like, start at the left of the diagram and work to the right.

i.e.
Unhook the starter circuit. Is the draw gone? If not ...
Reattach then unhook the 30A AM2. Is the draw gone? If not ...

If not, it HAS to be something OP or a previous owner wired directly to the battery, right?

However, if OP find unhooking the 30A AM2 circuit stops the draw, then two options: It's either down (A) the engine bay fuse/relay block or (B) the alternator circuit. So rinse/repeat:

Unhook the power to the alternator, ideally as close to the AM2 circuit as possible - it's possible the alternator is fried and shorting to ground OR the line to the alternator is nicked/compromised and shorting, which is why I say to pull the alternator wire as close to the power source as possible, rather than just unplug directly at the alternator.

If draw is not gone after detaching alternator, repeat for the Fuse/relay box. IF draw goes away, you know it's downstream from that box, and you'd need to repeat for every circuit inside, although I'd flip the box over and look for any shorts before that!

And yeah, that's a good point