[VetteVet]

All your experiments have one thing in common. No matter which power source you use for the orange wire to feed the dome light, It gets shorted to ground through the headlight switch.

The white wire is the ground for the dome light circuit even as stated by the AAW instructions.

It appears to me that the white wire is grounding the orange wire when you pull the HL switch knob out.

With the truck battery disconnected and not power on the electrical system, check for continuity between the white and orange wires when you pull out the knob. This is without the dome light bulb inserted. The orange wire should only have continuity to the white wire when it has the dome bulb inserted. Also the white wire is only grounded when either door switch is closed or the headlight switch is rotated all the way C/W.

The battery power fuse for the orange wire is the same as the red wire in the OEM fuse panel and should not affect anything, which it isn't if the brakes are working and the brake lights fuse is not blowing. The fuse panel from AAW is just expanding the number of circuits that are fused more so than the OEM panel.

The reverse lights circuit is one of the simplest in the whole truck. You have power to the reverse lights fuse and one wire from there to the reverse light switch and the same wire goes from there to the rear end where it splits and goes to each light. When you put the transmission in reverse, it closes the switch and power goes through the wire to the reverse lights.The manual transmission uses a switch on the transmission or the gear shifter and the automatic uses the neutral start switch on the steering column. Most of the GM vehicles use a dark green wire and a light green wire for this circuit.

I hope this helps you find the short. VV