87 F250 SCab, 460 Carbed, C-6. Oil pressure gauge dropped low, engine light came on a couple of times. Changed the sending unit things ok for a week. Yesterday oil pressure dropped -pegged the needle in the 0 position and engine light came on. No noise from engine. checked what I could and drove it 40 miles home. Today I started it to move it to the garage. OP up to normal. Disconnect the sending unit wire, OP on gauge goes to 0. Connect the wire OP normal. To me this indicates an open sometimes. Using a test light on the OP wire it lights faintly. Have to get a volt meter to check the voltage. Wish my shop manuals weren't 600 miles away.... The OP gauge dropping to 0 seems to have no effect on the other gauges.
Anyone have any ideas??

Am looking into a mech. gauge.

Thanks

 

That's the best idea right there! That will determine if is another faulty sender, bad dash gauge, or a real pressure issue.

 

Update: took the sender back to the parts store, Got another one, installed it.....pressure reads 0. Put the original one back in. Gauge reads normal. Returned "new" sending unit for refund. Ordered a Motorcraft one.
Forgot to mention earlier, this engine has a low oil pressure fuel pump shut off switch. So if no oil pressure the electric pumps won't work.