Oil pressure gauge not working

[K5Rob]

87 K5 Blazer, oil pressure gauge not working. Just did an LS swap, using the sender that was in it before. I had the wife sit in the cab as i grounded the connector and it came to life. Then i ran it for a moment and it was working fine. Also had that bounce when you turn the key. Now, nothing. Cant get it to do anything even when i ground the wire. I pulled the gauge out, it has 3 prongs. Tried touching them to a 9v battery and it does either peg or go to zero depending on which way I am touching the prongs. Wondering if its in the cluster? I am not an electrical expert but how do i further diagnose this?

 

[YakkoWarner]

If you have a sender with a 3 prong connector, two of those 3 prongs are for a fuel pump relay backup (they are effectively a switch that closes when there is more than around 5 PSI, originally intended to provide a secondary power feed to the fuel pump if the relay were to fail). Only 1 of those 3 prongs is actually the pressure sensor, and since I'm at work and the truck is at home I can't say which one off the top of my head.

 

[K5Rob]

If you have a sender with a 3 prong connector, two of those 3 prongs are for a fuel pump relay backup (they are effectively a switch that closes when there is more than around 5 PSI, originally intended to provide a secondary power feed to the fuel pump if the relay were to fail). Only 1 of those 3 prongs is actually the pressure sensor, and since I'm at work and the truck is at home I can't say which one off the top of my head.

The sender has one wire. The gauge has 3 prongs

 

[K5Rob]

I would like to rule out the gauge cluster. Is there a way i can check that the cluster maybe by checking the female ends that the gauge plugs in to?

 

[YakkoWarner]

OK I misread - I thought you had the 3 prong sender. I have no idea what 3 prong gauge wiring would look like, usually there is just 1 wire from the sender and a ground.

 

[K5Rob]

OK I misread - I thought you had the 3 prong sender. I have no idea what 3 prong gauge wiring would look like, usually there is just 1 wire from the sender and a ground.

??????
My sender has 1 wire
My gauge has 3 prongs. This is the oil pressure gauge in the cluster. If you take it out, there are 3 “prongs” on the back

 

[K5Rob]

My question remains. Is there a way to test the cluster. When i remove the gauge. Can i test the female ends that the gauge plugs in to.

 

[CountKrunk]

I assume you could check the cluster pins for continuity.

 

[83Stepper]

??????
My sender has 1 wire
My gauge has 3 prongs. This is the oil pressure gauge in the cluster. If you take it out, there are 3 “prongs” on the back

The 3 pins on the back of the gauge are for key on power (IGN), ground, and sender wire. Should be the same on most of the trucks and clusters pre OBD.

My question remains. Is there a way to test the cluster. When i remove the gauge. Can i test the female ends that the gauge plugs in to.

Yes, you can test for power, continuity on ground and the sender wire. The prongs on the cluster might be different than my 83. Top pin is ground, left lower is key on power (12v) and lower right is sending unit lead. Test with key on for 12v and ground. Process of elimination will tell you which is the sender unit wire. Check resistance on the oil pressure sender lead with key off, key on and engine off, and key on with engine on.

 

[K5Rob]

The 3 pins on the back of the gauge are for key on power (IGN), ground, and sender wire. Should be the same on most of the trucks and clusters pre OBD.


Yes, you can test for power, continuity on ground and the sender wire. The prongs on the cluster might be different than my 83. Top pin is ground, left lower is key on power (12v) and lower right is sending unit lead. Test with key on for 12v and ground. Process of elimination will tell you which is the sender unit wire.

Thanx i will give this a shot in a moment. Do you know if the boards go bad? Do i need to take dash pad off to remove
Cluster (thinking ahead)

 

[K5Rob]

The 3 pins on the back of the gauge are for key on power (IGN), ground, and sender wire. Should be the same on most of the trucks and clusters pre OBD

One other question, I DID use teflon tape on the sender (stupid mistake on my part) but i also know some of the threads inevitably cut through the tape. And like I said the gauge was working briefly. Now to rule out a ground issue, could I hose clamp a ground wire to the body of the sending unit (on the hex closest to the threads) and then run that to a good ground. Is there any reason that wouldnt work? This is on an LS motor (using original to truck SBC sender as previously mentioned) but sending unit is practically impossible to remove due to giant truck intake

 

[YakkoWarner]

You could also just for a test clamp a negative jumper cable onto the metal part of the sender and ground the other negative clamp anywhere you know is good as a test - if it works than go through the effort of making up your ground wire as described. A quick zero-cost test and if it doesn't work it saves you some effort.

Other zero cost test would be to ground the wire that goes to the sender, that should make the gauge go off-scale high. If it does, you know the wiring from the panel to the sender is good.

 

[K5Rob]

Okay well I got it working. With much messing around. Pulled the cluster and found there was no contact to the “board” behind it. Shoved some male spade terminals in there and now my gauge works. Of course i messed with the ground first. Took teflon off, reinstalled, no dice. And it leaked. Put teflon back on, no leak that i can see thus far (coolant mess now burning off) and the gauge works.

 

[83Stepper]

Okay well I got it working. With much messing around. Pulled the cluster and found there was no contact to the “board” behind it. Shoved some male spade terminals in there and now my gauge works. Of course i messed with the ground first. Took teflon off, reinstalled, no dice. And it leaked. Put teflon back on, no leak that i can see thus far (coolant mess now burning off) and the gauge works.

Yeah, usually it's just a bad contact issue, same with like 99.9% of the bulbs in the cluster that seem to work, not work, then work, then not work again. Glad you got it figured out!