One other possibility for that connector, which I totally forgot about, was the 203 case "lock"
under dash light. I remember seeing that single connector in many of my bronco's, but of all
the one's I had over the years, only 1-2 had the 203 case and they were both parts trucks.
1973 - 1979 F-100 & Larger F-Series Trucks - NP203 Lock Contact Switch - Folks, I posted this in the drivetrain forum, but had no response. I have a 77 F150 w/ NP203 Transfer case (full time 4WD). These trucks featured a simple spring loaded ball detent switch which turns on a light in the cab...
www.ford-trucks.com
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After more digging, it seems T-18 and 435 both used the same 2 wire connector, so the back up light thing is out.
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