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Is there any where on this site where I can find a wiring diagram for a 1978 F150.......or can someone point me in the direction of where I can find a diagram ??
I need to be able to follow the wire's from the back of the truck all the way up to the outside of the firewall where the 8 pin connector plugs in going into the inside of the cab.
Thank you guy's for the diagrams they helped me with the 8 pin connector I was looking for, I have another problem.
I checked the continuity in all the wires from the back of the truck in the wiring harness for the tail, stop and turn signal's and found the problem with my turn signal's.
I also found that the brown wire in that harness was shorted to chassis and the ground on the chassis. I followed it back up to the connector and it has a separate two wire connector right next to the 8 pin connector. The wire was not unplugged from the connector outside the cab while it was showing grounded to the chassis.
I was not able to find this connector in the wiring diagram, and was wondering where it plugs up inside of the cab, this wire should be the running light wire.
Thanks F 250 Super 4X4.......I will try and get a pic of the connector I should have said that it is green in color like the 8 pin in the same harness.
The other thing I didn't mention in my other post is that when I unplugged the connector and check continuity it was good on that wire.
I remover the harness from the truck so I could find the problem better.
Hello everyone, I'm in the process of finishing up my '78. I'm currently working on the electrical system. I'm not getting a signal from the ignition switch to the solenoid via the red/blue wire. However, the signal from the ignition switch/starter *is* reaching the red/blue wire at the IGN module. Can anyone tell me what that "NS BU" box is? Thanks in advance.
Regards, Bernd 61HD
I believe the NS stands for Neutral Switch and the BU stands for Back Up lights. Look right above the edge of your red circle. And it shows the wiring with a M/T only, which is the wiring bypass for a manual transmission. And that is by the means of a plug with 2 wires looped back to itself.
If it is a auto trans, then you have the NSS (Neutral Safety Switch) on the side of the transmission. Actually it is a have it in Park and or Neutral to be able to start the truck switch.
Manual trans has a NSS bypass [ictured below. The back up lights switch for a (manual trans) is threaded into the top of the trans mission.
Automatic trans NSS on the side of the transmission.
Last edited by 77&79F250; Mar 15, 2026 at 03:25 PM.
Hi, thanks for your reply and help. I figured it out now. The cable isn't installed yet. It has something to do with the cruise control. When the ignition is on, there's power to it.
Best regards, Bernd 61 HD
Glad to hear you got it figured out, and yes that yellow 3 hole bullet connector plug is a OEM 12V keyed power source. And yes that is the plug that powers the cruise control.
There is also another 3 hole bullet connector plug that is a constant 12V. It is on the passenger side, sort of generally behind the left hand side of the glove box. It is black and powers the glove box light, the cigarette lighter. 2 wires grn/yellow
Once removed from its bundle it has a lot of reach.
"Glad to hear you got it figured out, and yes that yellow 3 hole bullet connector plug is a OEM 12V keyed power source. And yes that is the plug that powers the cruise control."
Hi, thanks for the reply. I figured out the cruise control part. But where exactly is this cable with the round tab attached? It has to be screwed on somehow.
Regards, Bernd 61 HD
What is this "cable with a round tab" you are asking about, what is its function? And what system is it related too? Then I might know where it is located.
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