Getting closer to the answer, I crawl under the dash today, found 2 wires from the red light, one went to ground, the other (yellow) went through the firewall and laced through the frame to the plug at the hitch, it look as if the light is a add on by a previous owner, the wiring on the plug at the hitch looks as if it was a factory install. I didn't have time to check to which pin in the plug that the yellow wire went to, the plug is a 6 pin plug, 5 on the outer circle and one in the center. What a 6 pin plug is used for, I don't know. The hunt continues. My idea is, that once a trailer wiring is hooked up, the light comes on, if by chance the plug were to come unplugged the light would go out and the driver hopefully would notice that it is out. Any other ideas
Bill