You say you've checked the harness for loose wires. Have you checked the wire for the brake feedback with a multi tester to be sure it is activated when the brake pedal in the toad is depressed? The problem could be between the toad's brake light switch and the harness to the MH. It could also be a bad brake light switch, in which case you don't have brake lights on the toad. Had that happen last year in Michigan.
Mike & Linda Finnerty with Finn & Rosco (Golden mix brothers)