I have been researching this for like two weeks and finally was able to figure this out>>>
I bought my ARE shell about 9 yrs ago. It came with a flimsy light screwed to the aft end of the camper shell. It probably broke within a week, it was replaced with another flimsy light during a repaint because when I received the camper the color was way off. The light didn't last either. I finally got around to working on it because I cannot see anything in the bed when the shell is on. I managed to figure out the wiring for it. I removed the driver side tail light. Found the brake/tail light (green/red for brake light, solid green for tail light and the white/black ground all in the same socket. The installer had used the blue quick splices. There was a red power and a black ground wire from the 3rd brake light and a red power and a black ground wire from the dome light.
The red wires (power) went to the green/red (power for brake) and solid green (power for tail light) wires on the brake/tail light (same socket).
Splice #1 was the red wire (power) 18-22 gauge from the 3rd brake light on the shell to to the green/red wire (brake light power)
Splice #2 was the red (power) 18-22 gauge from the dome light on the shell to the solid green wire (tail light power)
Splice #3 was the black wire (ground) from the 3rd brake light to the white/black ground.
Splice # 4 was the black wire (ground) from the dome light quick spliced to the black wire (ground) from the 3rd brake light.
It took me awhile to figure out what they had done cause they had taped everything because the wire colors where faded.
I undid everything, got new wire red and black and Tap quick splices. I wrapped two lengths of the red and white wire in the smallest flexible conduit and wrapped it with electrical tape and then passed it through the little gap at the top of the inside of the tail light opening (it passes in the bed from underneath the rail. I pigtailed the black (ground) and tap spliced to the white/black ground, then I tap spliced the red (power) from the 3rd brake light to the green/red and red (power) from the dome light to the solid green.
My issue is that in addition to the original dome light. I want to add 4 LED strips two for the camper shell and two just for the bed when there is no camper shell. problem is I only have one red and black wire to connect 4 power leads and 4 grounds not including the original dome light power and ground. I know I will need a switch to control the LEDS unless I want them on all the time when my driving lights are on. Any and all ideas are helpful.