I'm getting conflicting info that I'd like to clear up if possible. I have an '01.5 2500 with the factory tow package. As I understand it, the trailer lights harness (turn, brake, marker) is fused in the power distribution box under the hood. Is the 12volt trailer harness power wire (charge wire) fused? I've heard yes and no..... which is it?

I'm getting ready wire the harness plug in the bed for my gooseneck and the trailer cable I'm using has a 10ga wire for the 12volt wire. If this circuit is not fused (or if it's inadequately sized for my needs) I'll run a seperate fused "charge" wire to the trailer harness plug in the bed. If I do this, I'll run that wire through a relay so that it is only energized when the ignition is on.

Thanks.

 

Nevermind..... I was able to locate some wiring diagrams and after sorting through was able to determine what I needed to know. Nothing like answering your own questions.....

Anyway, I'll state here what I found out in case it helps someone else.

Fuse 8 in the power dist. center is a 40Amp fuse that supplies 12volts through a 12 gauge conductor to pin 11 on Joint Connector 2 (JC2). Power is then split to pins 10, 12 & 13 of JC2.

Pin 10 is connected to a 12ga wire to the Electric Brake Provision which sends 12volt power (via the brake controller) on to the trailer tow connector (TTC). Now here's the frustrating part.... the factory TTC steps down to 14ga wire at the connector.

Pin 12 feeds 12volt power through a 12ga wire straight back to the factory TTC where, once again, the wire size is stepped down to 14ga just before the connector.

Pin 13 feeds 12volt power through a 12ga wire to the Trialer Tow Relay. The control circuit side of the relay is triggered by the headlight switch so that when ever the running lights or headlights are on, the relay is closed which feeds 12volt through a 12ga wire back to the TTC where, yup... you guessed it, the wire size is again stepped down to 14ga prior to the connector.

The backup lights signal, left & right turn signals, and brake lights for the TTC are tapped directly off the circuits feeding those systems on the truck.

So, to summarize:

• the 12volt power wire to the TTC is not isolated from the truck's 12volt system, but is fused through a 40amp fuse.
• the trailer running lights are isolated from the truck's systems by the trailer tow relay and are also fused through the same 40amp fuse.
• the electric brake feed is also fused off of this same 40amp fuse.
• the backup lights, turn signals and brakes are not isolated from the truck's systems and rely on the same fusing the trucks system uses.

What I can't figure out is why the factory TTC would step down the brake feed, power, and marker lights wiring to 14ga instead of leaving it 12ga all the way to the connector. When I tap into the wiring harness to run the connector to the bed of my truck, I will do so ahead of the splice for the factory TTC so I can eliminate the 14ga restriction to the power and brake feeds. The 14ga restriction to the running lights is not that big of a concern.