I have a C&C and had a megacab bed installed on it. The rear tailights are giving me issues..I purchased a socket from NAPA that fit the dodge taillight with a dual filament bulb. I used a 12V test light and I came up with this...

Left side
white w/dark green tracer - left blinker/brake light
white w/light green tracer - reverse light
black w/green tracer - ground
white w/yellow tracer - +12V constant

Right side
black - ground
white w/yellow tracer - right blinker/brake light
white w/light green tracer- reverse light
white w/gray tracer - 12V constant

I also have a trailer connector prong and 5 other wires...
These wires are
Pink - no power
Purple - no power
Red - no power
2x white w/brown tracer - no power

I tried hooking up the Napa socket with dual filament bulb on the "right side" as followed...
red - white/gray
white - white/yellow
black - black

With the light hooked up as followed I have no running lights to that bulb...the brake light works and turn signal works but the marker does not. Im not sure why...if anyone could help I would really appreciate it. Thanks guys.

 

With the truck being a C&C the lighting harness was done different. You need to establish where and how they tied the Megacab lighting into it.

A similar project was discussed on this thread:

https://www.dieseltruckresource.com/...p-t309915.html

Go to the link I posted and read up on the lighting requirements and harness layouts.