Had the same issue 2 years ago after installing a new stereo. Marker lights and all interior dash lights did not work. I pulled the dimmer plug and ran a wire from the power side of the dimmer to the accessory part of a toggle switch that I set up with seperate power and ground. I had originally bought a wiring harness to attatch the new cd player to the harness of the truck but it wouldn't work so I had to snip the wires and attatch them to the cd player wires. Somewhere in this project a wire that must run in series from the dimmer to control the brightness of the stock cd player must not have been reattatched. So now I can manually turn off and on the marker lights and interior dash lights by the flip of a toggle switch. This might not be the best way about it but it's been working for 2 years.