There's a plug on the driver's side of the trans near the back, or on the back end, where the switch screws in.
When the reverse gear is engaged, it touches the end of the switch and makes the circuit complete to ground and turns on the light.
Thank you, I know how it works, I just wasn't sure whether the 3 spds got them or not, the dash has no hole for it, and I know my 69 RR had it and my 73 Cuda but they were both 4spds...never had an A-Body before.