The best way to do this is to drill a new hole in your roof near your roof mount brackets and run the wiring down directly into the cab of the truck.
Running wiring for a roof top warning light.
Chances are if you want the roof marker lamps you re going to be running wires.
Do not just run the wiring loosely through the door jam.
Just got a silverado 2500hd duramax and am trying to wire a cab top magnetic red light for fire and rescue.
It s supposed to be used for a strobe flashing safety light.
Down the side of the windscreen glass.
Forget about drilling more holes and running the risk of damaging your vehicle when you already have holes for your factory lights.
This forum helped me find the wiring but is there an existing hole through the roof say under the marker light to get the wire from the light to the switch connection.
This is the best method because it is the shortest distance for the wire to travel and it has the least chance of getting smashed in your.
Running wiring from the roof is generally not a plug and play affair and will require some auto electrical knowledge in selecting suitable wiring gauge and the joining or termination of wires due to the extended length of wiring required in addition to the supplied wiring harness.