This is a big post. bear with me.


First off- out of the 4 wires in the last picture, 1 of them does not end in the same connection. Specifically the top left prong in the last picture goes to the bottom spade in the 2nd picture.
The other 3 prongs (in the 4th picture) go to connections in the 1st picture.

Is that correct?

Second off- what does the that connection go to?

 

 

These 2 ends are the same wire. what do they do? they werent hooked up...

 

Thanks everyone for the help and have a great Thanksgiving!!

 

You're kidding right?

Help us out with a bit more information.... physically where were the connectors on the truck? Engine compartment? Dash? Frame rail? Where?

What is the year, model, and configuration of the truck???

Did you trace the wires to where they originate? How about reviewing the wiring diagram applicable to your vehicle?

 

Sorry about that.
A-78 inline 6 4wd. The whole wiring I beleive is called the 'chasis harness'. It runs from the master cylinder all the way back to the taillights.

The first 3 pictures are up by the master cylinder. The 4th hooks into the tailight wiring.
the last picture was roughly where a 'midship' fuel tank would be.

and unfortunately Im not very good at reading the wiring diagram I have.....connection wise...

 

Reading a wiring diagram is like reading a map. It's time to learn!!!

Go to this page and refer to the 1979 wiring diagrams since the set for 1978 is not yet complete. 1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net

The seven-pin, eight-hole connector is likely connector #306 (C-306) on sheet 3. If you look at the lower half of that sheet, each box contains a location where the connector can be found.

I think that round plug near the mid-ship tank is for a 4WD indicator switch on the t-case... I THINK. Does your truck have a 4WD indicator lamp? I have a 73 so I don't have it but I recall some owners have also discovered that plug but it is not connected either. Refer to sheet 4, connector C-418.

... Otherwise, note the wire colors and find the corresponding connector with that combination.

 

ok new question for you. I have a bad ground; 2 exactly.

I have determined that the grounds for my taillights are bad for the following reasons
1. The harness was hooked to good grounds in the front and tested before running back under the truck. Everything worked.
2. I ran the left side lights to the ground screw for the fuel sending unit and that half works great again.
3. When i screw both grounds behind the taillights, i mysterously lose countinuity on my multimeter (creepy i know, exactly as it sounds)

I have taken some sand paper and sanded both down to shiny bare metal with no improvement. Im not sure what else to do.
The only thing i can think of is the bed. Its ROUGH, but that brakelights (only) worked prior to removing the wiring harness.

Ideas requested....im stumped.