Cruise control

[Kaiden]

When I plug in my cruise control box my passenger tail light goes dead

 

[Erik the Awful]

For any taillight issues, step one is to check your grounds on the rear harness.

 

[Kaiden]

The harness seems fine and all the grounds are good, the tailights work fine along with blinkers but once I plug the harness in under the hood the passenger one goes comply dead on running light function but works just very dim when brakes are pressed. I have even replaced the tailights and motherboard along with bulbs front and back.

 

[SAATR]

Brake and turn signal functions pass through the multifunction switch, as does the cruise control. I would have to find the specific portion of the schematic to check to see if the running lights also pass through that switch. Regardless, you need to check the malfunctioning circuits and see what's going on. Is it loss of ground, power on the ground wire, low voltage on the the supply to the lights, something in the CC harness back feeding or shorting when it is connected? A multimeter and a schematic are your way forward. You should be able to find an electrical schematic for your truck on this site.

 

[GoToGuy]

What year, make, model ? There are subtle differences between years. .