OK? Where is the fuse for the trailer 12v supply?

[cowboywildbill]

OK I'm and idiot!
We have a 2006 C/C dually 3500 Dmax. I think I might have blown the fuse to the tow package trailer wiring harness. The 12volt aux power for charging up the trailer batteries. When I check the contact at the trailer plug, I am getting 4.6 volts? That's strange why not 12 or 14 volts the same as the truck batteries ? I went all through the owners manual and I swear I can't figure out which fuse it is. Am I the only one that has a problem deciphering the manual? If it had a ryhme or reason to it, I haven't found it. I pulled every fuse under the hood and none were blown. I guess I could start pulling everyone at the drivers side fuse panel also. I always thought the fuses for the trailer supply were in the box under the hood.
The owners manual say's there is a fuse block located under the steering colum under the dash also? But I don't see it.
I don't feel too bad though, it took a GM tech 30 minutes to find one of the door lock fuses that had blown on our 02 dmax, he said it was a new one on him when he finally found it. I figure one of you techs would know right where this one is.
Any input would be appreciated. Thanks.

[DmaxMaverick]

It's in the underhood fuse box. It should be a 40 amp. If they didn't move it for 2006, it will be in the inboard row, but should also be marked on the box cover.

The reason for the 4.6V is a fuzzy one. 2003 and later models have a multiplexed electrical system, and many circuits have a diag. current on the circuits. The voltage may show 4.6 (supposed to be 5V), but it will have almost no current, and shouldn't even light a test lamp. Just enough to tell the PCM what's on the other end of it. I wouldn't think this circuit would have it, but it could. 2003 - 2005 don't have that circuit diag'd, but they may have changed it for 2006. I checked the book on it, and there's no mention of it being charged w/o a fuse in place. If it is grounding somewhere, it could explain a stray voltage, and maybe a blown fuse. It takes quite a bit to fry a HD 40 amp'er. Look for smoke.

[cowboywildbill]

Thanks, I'll look under the hood again. This 06 block looks like it is a little different fuse block than my 02. It is in same place and all, I just didn't see a 40 amp in the 06 block. I do recall one in the 02 though. I'll chck it again. Thanks

[cowboywildbill]

Thanks, I found it. It was the top left 40 amp fuse in the under the hood fuse block if you are standing at the left fender looking in. And it isn't marked on the cover either? Just shows stud 1 and then a blank spot to the right of that.
The fuse looked fine, but after looking at it with a magnifying glass I could see a very fine break in the copper. I only found that because I tested it with a continuity tester first and it didn't give me a closed reading. But it did read .002 or something like that. The break was almost invisible, I guess that might explain the 4.6 volts on my multimeter, but wouldn't light the test light. When I took the fuse out I had no voltage at the plug anymore. I guess the fuse was just barley conducting some current. Strange? Maybe it was a bad fuse and not blown. In the past when I have blown a 40 amp on our 02, it was smoked and pretty obvious. Thanks again for your help. Too bad the book doesn't show the fuse and it's function. I'll get a new fuse today and then see if I get full voltage at the plug. Thanks again D/Max for your help.

[cowboywildbill]

Replaced the blown 40 amp fuse and all is well. I have 14 volts at the pin in the connector. But when I pulled the fuse out again and re checked the voltage just for grins, I had 4.6 v at the pin again but with no fuse this time ? I had no voltage there the other day after pulling the bad fuse out. I thought it was a small amout going thru the blown fuse the first time. Strange? But I do have power to my trailer batts now, and I know which fuse it is if it blows again.
The original fuse blew when I tried to pull in our slide on the 5th wheel, which had totally dead 5 yr old batterys. The elec/hydraulic pump that worked the slide was too much for it to handle without charged trailer batterys. Thanks again

[JohnC]

My '06 came with a slip of paper attached to the trailer brake harness describing that fuse. The description was clear as mud, though, and I had to ask here before I figured it out...

[upsguy]

When I wired up my prodigy electric brake the instructions with the factory harness said the 40 amp fuse should go in the stud 1 position.

[cowboywildbill]

Thanks, I got the new harness but there wasn't anything attached to it. It wasn't in the glove box when I took delivery. I had to ask my dealer for it and for the diesel supliment manual, they keep them in the office I guess people take them when they test drive sometimes. It was in a plastic bag and Looked like it had been opened already.
I used my old harness off of my 02 since it was already wired up to my joran brake controller. I swapped the two pins so the wires in the 02 harness so it would work in the 06.
I really appreciate all of the help that I get on this forum, I have alldata for the 02 but it isn't available yet for the 06's. And I get better directions and advice from the D/P and all of you guy's than I usually find in alldata. Alldata is good, but sometimes it can be a pain to find what you are really looking for, especially when it comes to fuses. Thanks again for all of the input from everyone and especially DMaxMaverick. You guy's are great.