12 Volt Batt Fuse

Shawn T · April 4, 2005

Here is the deal. I installed the factory trailer brake wiring harness and added a trailer brake controller to my truck. That works fine. My problem is the 12 Volt supply from the plug to the trailer battery. I have used a test meter and there is no juice. I have posted this topic before and the replays directed me towards a 40 amp fuse in the underhood fuse box. Not it. There is not a missing fuse or blown fuse anywhere on this truck and I have yet to figure out where the trailer battery supply is. The manual or fuse legend does not help either. I tried to chase the wire back from the harness, but that is almost impossible. This wire should have been "hot" from the factory anyways. Somebody please help. I need that wire to run the interior lights on my enclosed trailer. I have been using it alot lately. Also it is about camping season, and it is sure nice to charge the trailer batteries while you are pulling it down the road.

Shawn T · April 4, 2005

GM Tech? I know you have the answer. Seroiusly though, starting to get frustrated with trying to trace it down.

GMCTech · April 5, 2005

From the driver's fender looking at the Underhood Fuse Block, there should be a fuse in the furthest upper right corner position.

That spot is held by a plastic "plug" from the factory, that gets replaced with the fuse that should have been taped to the trailer brake harness.

If the fuse is there, and still no power at the plug, remove the cover from the fuse box and make sure the wire with the ring terminal is hooked up to the post that is fed by that fuse. That wire wasn't hooked up at the factory until the 2003 MY, and even then, Ive seen some not connected for some reason.

Test that post for power while you are there.

If that is hooked up also, and you have power at the post, then we need to be looking for a broken or disconnected wire somewhere.

Let us know what you find, and we will try to add more info. if needed.

Hope this helps.

bigdogs · April 14, 2005

I added one of those female maxi fuses to mine but have not checked the trailer plug for power. Which pin is it supposed to make hot??

Shawn T · April 14, 2005

I added one of those female maxi fuses to mine but have not checked the trailer plug for power. Which pin is it supposed to make hot??

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I found mine also (Stud #1). I had to remove a red dummy fuse that looked just like a 50 Amp fuse. They had a bar code sticker across the whole row also. There was no way of telling until I removed the sticker. I feel like a dummy too. Anyways, the pinout is right on the plug cover. If I remember correctly, it is in the upper, right hand corner.

bigdogs · April 15, 2005

I'll take a look if there is a wire diagram on the cover and see if mine is hot. I replaced my dummy fuse with a 40A Littelfuse "female maxi" that I got from work.

Well I checked mine last night and it is hot even without the truck running so I guess my 03 had the wire connected at the factory and it only needed the fuse.