Here's my new project truck. Got it for $500 through a friend. It's got a rebuilt 350 and 4spd with maybe 3000 miles on them but the truck itself has over 1 million miles on it and has spent the past 14yrs exclusively on a farm. (same owner since 84) Its kinda rough looking and smells like rat piss (I'm not kidding) but all the mechanicals work.
1979 Chevrolet C20 Custom Deluxe Motor 350 bored over to 355. Muncie 4spd with granny low. 14bolt rear with 4:10 posi 1 ton springs Power steering & brakes. A/C Cloth interior & carpet
Work done: Replaced collapsed caliper hose. Re did wiring for non connected reverse lights. Installed new turn signal cam. Installed new headlight switch. Cleaned instrument cluster and replaced blubs. Replaced broken speedo cable 'Fixed' Rust holes.
Work to be done: Finish paint job. Replace mechanical window mechanism (its missing teeth) Fix sticky door lock. Fix leaking water pump. Get A/C working again. Replace all hoses and belts. Replace driver's door (its hanging low on the hinges and has bad rust) Fix broken exhaust hangers. Replace seatbelts. Oh and get rat piss smell out of the cab! lol
Assuming you have the muncie box (there was another 4spd as well) it's located facing the driver's side towards the rear and top of the transmission. I just felt around the transmission until I could feel the two metal prongs sticking out. It could probably be more easily spotted if you removed the transmission tunnel access cover but not required. Just run ignition power to the switch and then on to the reverse lights and your good to go.
I think my truck may have been rewired with an auto trans wiring harness because the reverse light wire ran from the reverse lights right up to the fuse box completely ignoring the transmission. I just cut the wire at the fuse box, patched it to ignition power and then spliced 2 wires off near the trans to access the switch.
Im away from home right now but I'll try and post a photo when I get home.