Flat towing

Glenn Dausch1 · May 23

Bought a 2025 GMC Sierra 3500 4x4 Denali to tow behind our motorhome. Was assured is was not a problem and even was showed protocol in owners manual. Went with the Demco Air Force one braking system since MH I designed to supply air to tow vehicle thus avoiding any electrical connections. Went with Etrailer plug and play wiring harness that connects into the tail lights. Also went with the Etrailer system that charged the batteries as well. When I go through the protocol of getting ready to tow and the electrical connections is made I have all the lights in the rear of the truck. The issue is when you put the truck in park the steering wheel locks up, obviously you cannot tow like this. What I did next is disconnect the charging line to the battery, this makes the towed vehicle protocol go perfect and I can tow the vehicle. The problem now is I have no lights on the rear of the vehicle. I think the problem is the module in the LED taillights, that need a signal rather then a 12 volt source. All the plug and play wiring from Etrailer have diodes in them. I have been getting nothing but the run around from the GMC dealer. Have called GMC help line and relayed exactly as above but not even a response. Ran into another person towing a 2500 and had the same problem, and the same response from GMC. He ended up putting magnetic lights on which look absolutely terrible. Any suggestions out there. As far as I am concerned I have a $90,000 vehicle which does not conform to federal standards. Is that a reasonable assumption

Transient · May 23

What's another $35 when you already spend $90,000?

johnnyquick · May 23

11 minutes ago, Transient said:

What's another $35 when you already spend $90,000?

What is the $35?

He is stating that it doesn't work properly, I see no mention of $35?

redwngr · May 23

I don't know what 'Demco Airforce One does or what your ETrailer system does.

Did you disconnect the battery with the shifter still in 'D"?

Edited May 23 by redwngr

Transient · May 23

1 hour ago, johnnyquick said:

What is the $35?

He is stating that it doesn't work properly, I see no mention of $35?

Magnetically mounted brake lights. OP did mention them.

Bikerjon · May 24

23 hours ago, Glenn Dausch1 said:

Bought a 2025 GMC Sierra 3500 4x4 Denali to tow behind our motorhome. Was assured is was not a problem and even was showed protocol in owners manual. Went with the Demco Air Force one braking system since MH I designed to supply air to tow vehicle thus avoiding any electrical connections. Went with Etrailer plug and play wiring harness that connects into the tail lights. Also went with the Etrailer system that charged the batteries as well. When I go through the protocol of getting ready to tow and the electrical connections is made I have all the lights in the rear of the truck. The issue is when you put the truck in park the steering wheel locks up, obviously you cannot tow like this. What I did next is disconnect the charging line to the battery, this makes the towed vehicle protocol go perfect and I can tow the vehicle. The problem now is I have no lights on the rear of the vehicle. I think the problem is the module in the LED taillights, that need a signal rather then a 12 volt source. All the plug and play wiring from Etrailer have diodes in them. I have been getting nothing but the run around from the GMC dealer. Have called GMC help line and relayed exactly as above but not even a response. Ran into another person towing a 2500 and had the same problem, and the same response from GMC. He ended up putting magnetic lights on which look absolutely terrible. Any suggestions out there. As far as I am concerned I have a $90,000 vehicle which does not conform to federal standards. Is that a reasonable assumption

This forum is for the 1500 pickups. You may have better luck posting on the HD forum.