So lets start here, 77' F150 rebuilt 351M & C6. Well my oil pressure was not reading on the gauge, gauge tests out good. Changed the sender, still nothing. changed the termination on the wire that connects to it, nothing. Then a very strange thing happened. When I shut the truck off the gauge shot up almost to the "H"??? re-start the truck, it flickers and goes back down to nothing??? I am lost here on this one, almost like it is grounded out. Does this make sense to anyone? This is the first electrical issue I have had, with this truck anyway.

 

You positive they gave you the correct sender? Idiot lights took a switch, which was standard equipment, gauges were an option, and used a sender. Never paid attention to a light-equipped engine (very rare up here, most everybody got the gauges - was told once it was a somewhere around $60 option?) - don't know what the switch looks like.

Might be worth checking with an ohm meter, assuming it's dead to ground when the engine isn't running, open when it has oil pressure, if it's a switch?

 

I just looked it up, and you might be correct. The one I replaced was a lot bigger than the new one.....That could be the issue, keep you posted when I get home.

Thank You

 

It sounds like it could be your sender wire. Follow it back to where ever the connector is, (near master cylinder I think) and check that out.



How did you test the gauge? By grounding the wire at the sender?
I had an '82 Mustang GT where the temp gauge would go straight to the hot peg, as soon as the engine was warm enough to lift the needle off of cold. I had read in Motor Trend, of all places, that that was a sign of bad gauge contacts. I pulled it apart and cleaned them, and it worked perfectly for the next 150,000 miles...

If your wiring is all good, I would try pulling the cluster and then loosening the contact nuts (one at a time) for the Temp gauge, and cleaning up the contact surfaces on the IP PCB and the contact nuts. You can back off the nuts a little, and then fold some 1000 grit or as high as you've got, and sand lightly in between them.

Probably just loosening and retightening the nuts will restore a good contact between the nuts/gauge and the IP PCB, if there is a problem there.

But if the posts/studs in the gauge spin with the nut when you go to loosen it, you can grab the end of the post with some needle-nose pliers, and go at the nut with a wrench. I was working on my '77 F150's cluster, and one of the posts spun in one of the gauges. and it freaked me out and I immediately tightened it back up - and it still works, so I don't know, maybe that's normal. None of my early Fox Mustangs ever did that...

 

If you go to Rock Auto, it looks like the Standard part #'s are PS18 for the light switch, PS60 for the gauge sender - and they have pictures. If the replacement was little, I bet it's the wrong one, the sender is kind-of a big clubby thing.

 

The oil pressure sending unit is large and dome shaped: E4ZZ-9278-A (replaced B7T-9278-B; C7ZZ-9278-A & C9ZZ-9278-A) Motorcraft SW-1547-B and was used on all 1957/90's cars, F100/350's, Bronco's and Econolines.