I have a 77 f100 302 stepside. that I bought in many pieces. Wiring harness was in the cab. I used the forum and my daughters 75 f100 as a guide. It was not running until yesterday. Very proud of myself I might add. Big step for me not for most of you guys though. The PO has installed an Edelbrock Performer 298 manifold and an Edelbrock Carb.
I have two wires on the engine that have not found a home.
I believe the red with a white stripe is for the engine temp sending unit. My first question or observation is that the manifold had a wire coming out of where the sending unit should be. This wire runs to the firewall and connects to nothing. Why would someone use a different wire and sending unit? Are the threads different in the Edelbrock? Should I splice them together and see what the gauges read (when I install the gauges) then rewire using the correct one?
The tan with red stripe I think goes to the oil pressure sending unit. The sending unit is not there, In its place is a small plastic hose that runs to nowhere. I did notice that it pumped out oil for the brief 2 seconds I had the engine running until I shut it down because I did not have a radiator installed yet. Where were they intending to go with this? There were no aftermarket gauges in the truck. I see that LMC sells two different switches. One for use with a guage and for use without. How would one know if the pressure is low without a gauge? Should I pick up a sending unit and install it using the original wire?
The "plastic line" is for an aftermarket mechanical gauge. The factory set up was either an idiot light or an electric gauge. Which sender you use depends on the instrument cluster you have. If you have a light, the sender can just screw into the port on the block. If you have a gauge, the sender is much larger and needs an extension to move the sender out and clear the oil filter.
As for the wiring, I would get the correct temperature sending unit and use the factory harness, the wire color is white w/ red trace for the oil pressure sender and red w/ white trace for coolant temp.
There is a separate wiring harness for the gauges and ignition called "engine gauge feed harness" it plugs into the main harness behind the engine at the firewall.