My 2006 Chevy Express 3500 didn’t have power to the factory trailer plug at the rear bumper. The fuses for the trailer plug (at 13 and 50) were good, but still no power to the plug for the travel trailer. A study of the internet revealed that some GM trucks, with the factory trailer package, came from the factory with the power connection for the trailer plug disconnected near the fuse box. This probably makes sense to some GM attorneys somewhere, but makes no sense to me.
I opened the hood on my Express van and looked for the unattached connection. I didn’t see anything obvious and was a bit disappointed. Then I reached down and started feeling around the wiring leading away from the fuse box on the inboard side and, Good God, there it was!! It’s folded underneath where you cannot see it.
Bring the connector out and clean it up for a good clean connection. There is a an unused post on the inboard side of the fuse box. Get your multimeter out and set it to DC Voltage. Start your van and put the negative lead on body of the alternator and the positive lead on the unused post on the fuse box. You should see at least 13 volts. Hallelujah!!
You will need an M6x1 nut to attach the connector to the post. Now, take the multimeter to the trailer plug at the rear bumper. Check for 13 DC Volts at the positive post at the one o’clock position and the negative post at the seven o’clock position, with the engine running. Happy trailering people!!😃👍🏁🇺🇸I hope this helps someone. The above took me a week to figure out. Hopefully, you get it faster than I did.

 

Thanks for sharing. That can be really frustrating. Can't imagine why they would leave that disconnected. I can see it being shipped that way as a lot of systems have to be connected at the dealership when the vehicle is received by the service dept. At least that was how it worked at the import dealers where I sold cars in the past.

You'd think a 3500 would be expected to tow something without special prep. It doesn't look like there was ever a fastener on that terminal.

 

That would make sense, that it was shipped not connected for safety, and the dealership didn’t check it. I had an ‘05 2500HD pickup that it was connected upon purchase from the dealer. That is part of why this issue had me stumped for a week.