The service manual shows the power comes from the fuse box on the "accessories" fuse. It's a 20 amp fuse. You can check it with a test lamp or a volt meter, power when the key is on.
The light green wire at the switch (power) will be connected to an accessories plug under the dash that will be an orange coloured plug with 3 "bullet" connectors. The dark green wire from the switch then goes to the road lamp bulbs
I can look at my Cuda later today for the fuse exact location if you need it
The row of fuses in the fuse box that are closest to the accelerator pedal, the second down from the top is marked accessories. I pulled that fuse with the road lamps on and they went out. Hope this helps to solve your problem.