77 F150 4x4 Manual Trans.

This blue wire with single pole rubber connector was just wire tied up under the cab by the PO. It is not connected to anything. It is located on the drivers side chassis at about the back of the cab. It comes out of the wire harness under the hood on the drivers side and runs back down the chassis along with the fuel sender and tail and running light wires which continue on back.

Thanks for your help.
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I recall it is for a fuel level sender if the rig was equipped with more than one tank.

 

I have one of those mystery connectors as well. I have two tanks and all the necessary connections are there. Looking forward to the answer................

 

It is for the lock light on full time 4wd trucks.

 

The wire is inside the canvas/cloth harness insulation with the other wiring for the bed. I think that the canvas wire insulation must have come from the factory but I could be wrong. I don't have full-time 4WD and I have the bed off and there is no evidence that there was ever an auxiliary fuel tank.

 

That is the connector for the 4WD lock light. It was used on vehicles that have full time 4WD. Your truck has part time 4WD so it doesn't have the light, but both trucks used the same harness so you have the wire, there's just nothing on the transfer case for it to plug in to.

 

OK. I'll just tuck it back up in the frame. Thanks for your help guys.