UPDATE: I found a 'Tow Board' in this coach which allows you to change a jumper and send a separate brake light signal to the toad pigtail (for toads with separate turn sigs). Switched the jumper and, sure enough, I found the wire that has the brake signal. I jumpered a wire from that to the + of the LED high mount light. Now when I apply the brakes, the LED flashes on/of quickly when the brakes are applied but will not stay on with the other brake lights :?
So, for any electrical experts....should I now try installing a relay and use the brake light signal to activate the relay to power the LED? I have plenty of other 12v sources in the engine bay.