Tow Vehicle Electrical Problems

[TXMAX]

I bought an '02 4WD 2500HD D/A in place of the '02 2WD one I had originally but this one has an electronic ghost.

Ever since I bought it the trailer running light fuse would blow when connected to a trailer. I bought a test device to try and find the short but now I have no trailer circuits working. The fuses under the hood are good except for the running light fuse. The owners manual refers to another fuse box under the dash but I seem to be too blind to find it that has what appears to be a trailer master fuse in it but like I said I have yet to find it. The truck has a brake controller in it from the previous owner and until this latest debacle it did work and activate on the 5th Wheel and boat trailer, nothing is activating now. Any suggestions are appreciated.
Thanks,
Mark

[BozDMAX]

How many trailers have you tried it on? If more than one trailer, then 99% it is in the truck.

Which plug are you using? I have one plug back at the hitch and another in the bed (called 'camper wiring', on the options list it is UY2 and will be listed on the glove box sticker). Check the plug(s) for a short and maybe even pull your plug(s) apart for a good visual inspection.

If you have not yet found a wiring diagram, most if not all are available at alldatadiy.com, a good resource for anything that would be in a shop manual. Well worth the $25 if you ask me.

Track the wiring harness back from the plug and disconnect any connectors and try for shorts again. As I recall, the little door on the trailer plug will tell you which wire is which.

Good luck - wiring problems can be the quickest trip to the funny farm...

[christo]

TXMAX

Would they be refering to the fuses inside the cover on the left side if the dash?
Beside the door on the verticle end of the dash.

There was a change made for the trailer brake harness wiring junction box that is behind a plastic cover near the drivers left foot.

I think this change took place during the 2001- 2004 model years.
Check with your dealer on this.

CHRISTO

[TXMAX]

Gents,

Thanks for the responses. I have tried more than one trailer, boat and 5th whl with the same results.

I'll look more carefully for the kick panel fuse box.

Thanks again,
Mark

[HowieE]

First get a wiring diagram of the female receptical on your truck and test for voltage at the terminal for the parking lights while the parking lights are on. If you do not have voltage at that terminal you have to look within in the truck, fuse or broken wire.
If you have vlotage at the receptical the truck is OK. Remove all of the bulbs in the parking light circuit of the trailer and test for a short to ground from the parking light tab in the plug. With all bulbs removed you should see an open circuit. If you see a short at this point the problem is in the trailer wiring. If you do not see a short plug the trailer into the truck and with the parking lights on start replacing the bulbs one by one. If you loose power after replacing a given bulb I would study that last socket for a problem.

[Dave]

There is a second electrical pannel under the dash beside the one next to the door. It is up under the dash above the parking brake. It is where the trailer brake wiring harnes plugs in. If memory servers me correctly their is a realy in that pannel for the trailer.

[letsgo]

Obviously You have a short circuit if the fuse is blowing,

TEST get the rear of the truck by the trailer tong, but do not plug in, take a ground wire and hook up to truck ground and trailer ground,

NEXT set a volt meter to 30vdc or more, we are looking for 3 separate readings on the meter.

0 vdc open circuit
12 vdc load in circuit, or ground (short circuit)
24vdc the battery on the trailer is hooked up backwards

there maybe larger fuses on the trailer (protecting their individual circuits) than on the truck, so the truck fuse being of a lesser value will blow first, but not allways as fatigue in a fuse link can be a (blowing) factor.

take your volt meter and find a live 12vdc wire at your truck plug, then find a 12vdc live wire at the trailer plug,

NOW take a voltage reading of the two 12vdc points with the (ground wire still attached), the one on the trailer and the one on the truck, you should get a ZERO 0vdc reading (correct) if you see a 24vdc reading the trailer battery is hooked up backwards

just a starting point if you still have a problem.

good luck