Thanks 1Ton. It is in pretty rough shape, so it probably has just been hanging there. Maybe you can help me another wiring question. I am adding a neutral safety switch to the new c6. It has two red/blue wires, a black/red and a white blue. I understand the black/red goes to the brake lights in the rear. Do you know where the others go? I was hoping it would be the same deal, that they put the plug in all the harnesses, but I don't see it.

 

5851

I understand the backup on the 4 speed had two wires

 

Yes, as far as I know, all the backup lamp switches (the ones mounted to transmissions anyway) had two wires.

For the NSS, is your trans a "newer" model where the neutral safety switch mounts to the side of the trans, around the shift-shaft?
If so, that's the easier one to wire in to your '79's harness. Which should already include an NSS connector up behind the engine near the firewall? Anything there, or are those wire colors you're mentioning, from the body side of the harness?
No matter what though, the Red w/blue stripe wires are the NSS wires that run from the ignition switch on one branch, through the NSS and then on out to the starter relay/solenoid on the other branch.
The outgoing branch to the starter relay attaches to the "S" post on the side of the relay. You should already have this wire in place, and then at the connector behind the engine there should be a short jumper wire connecting the two halves of the circuit.
The manual transmission trucks had only the connector and jumper. This essentially connected the ignition switch directly to the starter relay.
An automatic and it's NSS, used the NSS on the side of the transmission to either open or close this circuit. So in Park and Neutral, the connection is available to the ignition switch. While in any other position, the NSS is open and no power can reach the starter relay.

The Black w/red wire is the traditional backup lamp wire color. On older trucks, it was Black w/red on both sections. Maybe on later trucks they changed the other to White w/blue to help users figure things out.
I don't have a diagram in front of me, so you may have to test which one gets power with the key and which one does not. But even here, it really does not matter which one is which (usually) because it's just an open/close switch. As long as power gets to the backup lamps at the right time (when the shifter is in Reverse obviously) then all is good.

Did you find a connector behind the engine that might match the connector on the end of the NSS harness?

Paul

 

Thanks 1 Ton

This is very helpful. I have looked for the connector, but did not find it. I'll look again. The wiring in general is in pretty good shape. If it was ever there, it is probably still there. I have not found a spot that it has been butchered up. Do you believe the connector was included on all trucks, regardless if they are manual or automatic? You asked what color the wire was to the mystery plug I originally asked about. It is blue (maybe purple)

 

Yes, pretty sure that, at least for '78 and '79, the entire harness would have been there no matter which way the truck was optioned. Some harnesses changed, but for things this common and minimal I'm sure Ford would have included it in all trucks. And we've talked about the jumper wire here many times. So pretty sure your truck "should" have it.
Now where's Rich (77&79) when we need him?

What connector does your new NSS have on the end? A 4-wire square rubber plug? Something different? Got a pic?
Either way, look for the matching plug. Usually it's on a short leash, so should hang there behind the intake manifold. But if it's a longer one, perhaps it's fallen down behind the bell housing?

Paul