I have a 79 2wd factory 460 pickup. The original motor was no good so I bought a 76 with its original 460. I have the motor and trans swapped in. There's a small wiring harness coming off of the coil and such. The wiring has a square 4 blade connector and a flat 4 blade connector. I can't seem to find a spot on my 79s wiring harness to plug these into. So I'm assuming the wiring changed in those few years. Can anyone point me in the right direction as to how to hook up the 76s wiring to my 79s wiring? Also I read something about the neutral safety switches being different between 76 and 79, can someone tell me easiest way to get the 79 nss to work with the wiring on the 76 transmission? Thanks

 

Hope this helps? And maybe this? When the trucks came with a manual trans, there was a dummy plug used to bypass the NSS switch. I've never been able to come up with a part number for the dummy plug. To bypass the automatic set up:*Unplug the switch and discard or ignore. There are four wires in the harness plug, two each, red w/ blue trace and black w/ red trace. Run a jumper between the red/blue and red/blue, do the same for the black/red. That completely bypasses the NSS switch. Your truck will now start*and the back-up lights will be permanently on. Now on to the backup lights.
In the engine compartment is a little U shaped jumper wire. It'll be located on the drivers side splash pan, just in front of the firewall where the wiring harness comes through. Unplug the little jumper, this will shut off the back up lights. There should be a back up light switch on the trans cover. Run two wires from the switch to the two wires that were jumped. This will get your back up lights working again.
Just a note, you could make a jumper plug out of the NSS. Cut the switch off the harness and splice the two pairs of wires. I just hate to cut these switches up. New, they're getting pricey. Here's the little jumper in the engine compartment.
EDIT: If you don't care about the back up lights, just jumper the red w/ blue trace wires. This will by pass the NSS but the back up lights won't work.

 

Thanks so much, I figured everything out thanks to those pics. Next question, where do the 4 wires go to that come of the firewall through the drivers side of the a/c and heater core firewall box? I'm guessing they're for the a/c compressor but don't know. It was all torn apart when I got the truck

 

We at least need color ID, are they a 4 pin connector or what?

 

Ok so here's 2 pictures. In the first is a blue wire and a black/yellow stripe wire coming out of a plug in connection. Then there is the the square connector that has 5 wires. Pink, yellow, yellow/black, black, and maybe purple?

In the second pic is a group of four wires coming through the firewall and a/c n heater box. One is orange and goes all the way to the grille and has a round push together connector. One is a black ground, I can figure that one out lol, one is a thick black wire with a square push on connector which I assume if for a/c compressor. Last wire is a gray? Short wire that has a square connector. I'm think carburetor?