When I checked about using an overdrive 500 in my 50 Merc, I found that the early 500's only had one or possible two (can't remember) wires that controlled the on off of the overdrive, and they didn't have the lockup converter, but you have to have a switch to turn it on or off in the car because it is normally controlled by the trucks computer, I don't remember what the other wire was for, but it wasn't for the overdrive, it was for reverse lights or neutral safety or something, it's been a long time since I had the tranny sitting here, I decided to use a 4spd in the car so I sold it.
The cruise control switch is just to turn the overdrive off when you hit the brakes or slow down, not anything to do with cruise control itself. Several of the Street Rodders I talked to about it said they just use a toggle switch to turn the overdrive on or off, but I thought using a toggle to turn it off would be a hassle and I figured a way to have it turn off when you tapped the brakes by using a cruise control switch, it would also be safer.
