12 Volt Power to Trailer Connector Stopped Working on a 1998 GMC C/K Series Dually Diesel

Question:

1998 GMC dually diesel pickup On the lead that charges the battery from the truck to the battery in the trailer. This lead should charge the trailer battery at the same time as the truck battery when the vehicle is running via the alternator. My question is that in between and under the dash is some type of a silver resistor or something that has gone bad and wont send 12 volts thru to the trailer battery. Do I need this part and if so what is it?

asked by: Don J

Expert Reply:

What you might be seeing is a circuit breaker that has been tripped and is not allowing power to go through. On the C/K series trucks like your 1998, the 12 volt charge wire is connected from the battery and should be run straight back to the trailer connector. What may be the problem is a tow package fuse or relay that has gone bad and needs to be replaced. Consult the vehicle owners manual for all of the fuses/relays related to the tow package wiring.

If the 12 volt circuit was wired after market, you could bypass the wiring you have under the dash by connecting a length of wire, # 10-1-1, from the 12 volt pin on the trailer connector all the way up to the truck battery. Attach it first to a 40 amp circuit breaker, # PK54540, and then use the left over wire to go from the breaker to the positive battery terminal.

The 10-1-1 wire is sold in 1 foot increments so you will need enough to reach from the front to the back of the truck. Route the wire under the truck but avoid areas that may pinch or burn the wire like exhaust and suspension components. I have linked an FAQ on hardwiring a brake controller that has a section on routing wire from the front to the back and the circuit breaker that should help.

expert reply by: Michael H