I'm trying to work out some mystery wire / connector issues. In the engine compartment - driver side, near fire wall, I have 4 connectors. Two of them have nothing connected. The other two only have one wire connected, but multiple female ports. Can you help me identify these?

For context, I have a '78 F100, 302, MSD ignition setup, and some aftermarket gauges. Also, the truck has factory heat and had (now removed) dealer AC.

Cluster:


Unknown #1 - the only connection goes to my MSD 6A Ignition. What are the other ports for?


Unknown #2 - nothing connected


Unknown #3 - Nothing connected


Number 4 - I believe is the C-220 unit. Only the water temp wire is connected. The oil pressure port is empty, and I don't know what the 3rd port is for. FYI - my dash oil pressure gauge does not function - likely because they replaced it with an after market pressure gauge.




Thanks for any insight!

 

Unknown #3 (I believe) is possibly for the reverse lights or NSS, if it is a manual trans. Some times that one has a jumper.

" 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.

 

As always, I'm impressed with your knowledge! I'm a little lost though. I don't see a jumper wire for the #3 unknown. I also don't have a wiring harness with 4 wires - red w/ blue and black w/ red. It's hard to tell the original wire colors from when the engine bay was repainted at some point.

I need to check my back up lights. I checked my brake lights, turn signals, headlights, etc. when I got the truck, but I don't recall checking the backup lights. Once I get new spark plugs installed, I'll check that.

PS - this is an automatic trans.

 

Just comes from years of FTE reading, copy pasting information and being a Ford Truck Enthusiast.

I gave you the whole shooting match on those wire colors and stuff.

 

Sure, I appreciate the info. I'll dig a little deeper. Maybe my wiring color scheme is a little different. Thanks again!

 

The number 1 plug looks like it's one of the Duraspark ignition module plugs. Since you have an MSD ignition, your ignition module was probably removed. It was originally mounted on the driver's side fender in the engine compartment. Your MSD ignition is getting the power through that pin... The others are of no use to your system.

 

Take a look at these
1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net