Hi all, my son and I picked up 1978 F100 as project truck. The previous owner put in a 1971 400 in but did not finish connecting everything. The title shows as an F100 but it has 4 wheel drive chassis and I am thinking it may not be original to the cab. Anyway, to my question, I have couple of connections coming out of the cab next to the brake booster that I cannot find their mate. Coming from the cab there are two green connectors and one grey connector. Coming from the frame I have completely different connectors. I am fairly certain the green connectors are for the taillights and trailer wiring. Please see the attached pictures for reference.

Questions that come to mind, maybe an older frame with older wiring which does not match the cab?

I am not the strongest in reading these wiring diagrams and really appreciate anyone’s input in identifying these connectors and possible best solutions for correcting this issue.

Cab Wires

Frame Wiring

 

Sounds like you’re on the right track. If you have the build tag on the inside of the drivers door try checking that to see if you can figure out the options original to the cab.

Off memory, I think the green connectors in my 78 are specific to the original cruise control. For some reason the pictures weren’t loading for me, but I’ll check back and cross reference to my diagrams.

 

Thanks for the reply. I determined the grey three prong plug is for the cruise control. That just leaves the the green ones. It seems like I’m missing a small harness that connects these all together? At a loss at this stage.

 

The gray three terminal connector C-327 shown in the pictures is NOT for cruise control. It is for emissions related throttle actuator on the carburetor. Wire colors should be Red w/yellow stripe, Red w/green and black.

The Green two terminal looks like C-338, If it has a Brown with white and a brown wire, it is for the dual fuel tank selector valve and solenoid.

The green 8 terminal connector looks like C-306, it handles brake warning switch, fuel tank sending units and fuel gauges. Two terminals should have nothing on them. Wire colors should be pink/white x2, blue, green/red, black/red, yellow black, gray.

The brown oval connector with flat end And the one below it similar shape looks like c331 (blue and Red/yellow wire) or c-330 for the throttle kicker ( same colors)

The brown rectangular two terminal connector looks like c-611 for ac blower motor. Should have a black/yellow and black wire.

The square four terminal connector looks like c-801 which handles front marker lights and turn signals. Should have brown, gray/black, red/black, and white/blue or green/white wires


Some of these like C-801 and C-306 if identified correctly by wires colors, are necessary. Others will not be needed with an older non emissions engine. I use the wiring diagrams all the time. the best details are on the ones here... https://www.fordification.net/tech/wiring.htm

If you use diagrams from a haynes or chiltons they are not as detailed. The ones that I linked are physically from ford shop manuals, body builders book I believe is where I have seen these. They show what the connector numbers, on the same page as where the wires are routed and shown on each main diagram page and tell you where the connector is located in most cases-like LH Fender Apron at dash panel.

Check the wires colors and see if they match what I listed to confirm that I identified correctly and get back to us. Try printing or following along on the diagrams and i think once you learn to use them they will be super useful.

 

Thank you OrangFord! I really appreciate your help. I’ve download the electrical diagrams and they make sense.

I ran out of time today but I was able to confirm the 8 pin green connector has the following wires:Purple White X 2

Blue

Green/Red

Black/Red

Yellow/Black

Green

Huge win we now have that identified! Now my question is where do I find that connector or harness. I’ve done quite a bit of searching and came up with nothing available so far.

I did find the harness that runs from bumper/lights to the cab so maybe there are more wires tucked in somewhere. Holding on to hope on that one!

 

Look under the fender apron and or around the frame below there.