2023 Sierra 2500 HD Electrical Issues

[Magnolia Mama]

We recently had a gooseneck hitch installed in our 2023 GMC Sierra 2500HD. When we picked the truck up the electrical was FUBAR:

• Gauges bouncing up and down
• Wouldn't start when pressing the button but then started while just sitting
• When blinkers are on they work from the outside, but inside they either don't blink or go off and on our of pattern
• Dash screen at the steering wheel flashed between "Service Park Assist System", "Park Assist Off", "Service Park Assist System", "Service Trailer Brake System", etc
• A/C will not blow cold air
• Truck will lock itself but won't unlock when hitting the button on the door handle
• Dash screen in the middle constantly flashes the climate status (climate off, temperature set, etc)

 

We brought it to the dealership and they can't figure out what is causing this issue. We brought it to the hitch company and they rechecked all of their work and confirmed that no wires were accidentally cut or messed with and they did not do anything with electrical other than plug into an existing factory made connection.

 

Any ideas what the problem could be?

[the8rotor]

Whoever installed that hitch screwed it up... bring it back and demand it fixed. If the truck was working fine before the hitch install, it is their responsibility to make this right. 

[NWStever]

If the hitch installers did not disconnect the battery (batteries) before starting  the installation they may have accidently zorched a module of one type or another when mating the connector.  Did they confirm pin-outs (with the vehicle and accessory wiring diagrams) before making the connection?   Good luck troubleshooting. It is unlikely the hitch installers will have the requisite knowledge and skills to accomplish this.   

Edited April 27, 2025 by NWStever
correct grammar