If you are up to removing the gauge from the dash, it's not to difficult to test. I have only opened up the fuel gauge/ammeter, so I can't say for sure about all of the wiring, but if you open up the meter, you can confirm the following.

If the oil pressure gauge works like the fuel gauge, you have the Yellow/Red wire providing 12 VDC+. The gauge probably works on a voltage divider with one part of the gauge wired to black and the signal wire for the gauge wired to Yellow/White. (It says Yellow/White in the FSM, but it may be Yellow/Black in reality.) Get a 0-100 Ohm potentiometer and 2 6 VDC lantern batteries and wire them up to the gauge as shown in the picture. Vary the resistance on the pot and look for movement in the gauge.

By the way, you didn't use teflon tape or some other sealant like that on the threads, did you? You should only use a sealant that has enough metal in it to be conductive. Also, it's a good idea to have an ohmmeter or multimeter rather than a test light. A meter will give you a better quantitative answer.

After replacing 2 senders,substituding all the wires (power,ground & sender),trying another

known good gauge,it turned out that the 2 "NEW" senders and old one were all bad. Ordered 3rd new one from Motor Sports screwed & pluged it in tonight & BAM with the key

on it moves to zero & after engine starts it starts to read oil pressure (what a novelty!!)

So thanks Beerman,Steve & Others for your help!! Mahalo Plenty

Wow, I thought I was unlucky with two bad sending units. Too bad you had to go through all that extra work, but great it is up and running.

Phew! I am glad you finally solved the problem. It sure is tough to solve problems when you get so many new parts that all turn out to be bad. I hope you were able to return all the bad parts for a refund.

Old adage is "New doesn't necessarily mean good".

Sucks you had to go thru all that to find out, but glad you solved it.

Wait, sorry to bring back an older thread, but the sending unit cannot have teflon tape on it?

Wait, sorry to bring back an older thread, but the sending unit cannot have teflon tape on it?

The tape will insulate the sender. It needs a path to ground via the engine.

Looking at the wiring diagram, I see that you are right!!

I cannot believe I never thought about that. May explain my sluggish oil pressure gage.

Agree sorry bring up an old thread. I dont even have the oil pressure sending unit connected and the gauge reads full sweep no matter what. I obviously have some oil pressure since its rebuilt but not sure if its my guage or not. Someone in the earlier posts stated they had a bad tach and that contributed to the issue. I have a bad tach, it reads but very inaccurately for whatever reason. It worked at one point then got fried. So just curious as to what the issue is? Whether it is the guage or a faulty ground. I want to start by taking it out the dash and cleaning the connection.

Agree sorry bring up an old thread. I dont even have the oil pressure sending unit connected and the gauge reads full sweep no matter what. I obviously have some oil pressure since its rebuilt but not sure if its my guage or not. Someone in the earlier posts stated they had a bad tach and that contributed to the issue. I have a bad tach, it reads but very inaccurately for whatever reason. It worked at one point then got fried. So just curious as to what the issue is? Whether it is the guage or a faulty ground. I want to start by taking it out the dash and cleaning the connection.

It sounds like the wire that connects to the sending unit has shorted to ground somewhere. Trace the wire back from the engine to the meter and look for a bare spot in the insulation (cut, slice, pinch, etc.). The holes where the wires pass through the firewall is a likely place for a problem if the grommets are rotted away.