I'm trying to figure out some unplugged wire harnesses under the hood and what used to be plugged into them.


They're all in the same area right by the driver's side firewall.


The first is the light gray plug towards the top right of the photo. Lots of wires on this one.


Second, is the black plug in the middle. It has an insulated 90 degree elbow with a black and white wire.


Third, is the circular black plastic plug towards the bottom left of the photo. I believe it has two black wires


Any help would be great.

 

The "L" shaped plug in the middle is the back up lights. If your truck is 78-79, there should be a harness that comes from the NSS switch to the plug if you have an automatic or 4 spd. If you have a 3 spd column shift, that plug should plug directly into the switch.
If you have a 73-77 with an automatic, there should be a factory jumper wire plugged in to the plug.

 

Wiring Schematics here: 1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net

Need details on the vehicle so we know what we are looking for. With that said, I don't think the grey plugs are factory.

 

Duh, I guess the year would help.


It's a 1979 F250 with a 400 auto.

 

I guess that's why I have no reverse lights. Is the "L" plug the harness that you are referring to coming from the NSS switch? If so, what should that plug into?


I believe the gray plugs come from a man harness. They are not individual harnesses. Thank you for the wiring diagrams.

 

Could any of these plugs be related to cruise control? The PO removed the servo but I think there are different plugs for the servo.

 

No, The "L" shaped plug is part of the main wiring harness and goes to the backup lights themselves and not the switch.
Depending on whether you have a 4 spd or automatic, there should be a harness that comes from the side of the transmission (automatic) or the top of the transmission (4 spd) and it would plug into that "L" shaped plug.
On a 4 spd the back up light switch is towards the top of the tranny and screws into it. On the automatic, the back up lights and neutral start switch are combined in a single switch mounted on the driver's side of the transmission, it surrounds the gear selector lever.

 

You do know there are wiring diagrams in here right? https://www.ford-trucks.com/forums/1...then-some.html Start about post #10..

 

Great! Thank you for the information. I will start looking for the rest of the harness and trace the other two harnesses.

 

So you got me curious, I went out and looked and I have the same three connectors just dangling on my truck as well.

I've been going over the diagrams. I think the round one is for a differential lockout indicator lamp. Whatever that is

Still looking for the other two

 

Used on trucks with full time 4WD. Shows when the transfer case is locked.
Mounts under the dash, above the trans. tunnel.

 

The 3 pin connector looks like connector C-327 from the referenced diagrams which connects to a throttle actuator and carb vent solenoid. Emissions related stuff.

The round 1 wire connector is for the transfer case lock light. Only used if you have a full time transfer case NP203. C-417 on diagram.

The 2 wire 90 degree connector looks like C-1017. Goes to reverse light switch only if using manual 3 speed or 4 speed trans. If you have an automatic the reverse lights work off the neutral safety switch which should have a connector on or near firewall centered behind engine.

 

Thanks for this great information. I haven't been able to find the other part of the back up harness yet. I'll be doing more searching today.

 

Makes sense. since I have a 460 with no emissions stuff, part time transfer case and a C6.