I posted an electrical question on a forum but no one seems to know. I have an 1981 K5 Blazer that the previous owner put a big block in. I'm trying to get the factory gauges to work but I am having a tough time with the Oil pressure sending unit wiring. I found the oil pressure plug on top of the bell housing and pulled it out ready to plug into a new oil pressure switch when I notice the middle wire is cut and missing (see photo) and am wondering, it's just a two prong plug but there are three wires coming from the connection. Can someone tell me what this middle wire is too.... is it just a ground? Does it need all three wires connected to make the gauge work?

Oil pressure sensor connection plug

 

If I had to take a guess,it is back up power to the fuel pump relay. My 89 S15 Jimmy the oil pressure switch provides back up power to the fuel pump relay. Looks like the same color wire and looks to be tied together.

89 S15 Jimmy 4.3 Fuel Pump Circuit

 

Thanks for that. You may be right. I can't seem to find a schematic for a 1981 Blazer.

 

I would check the fuel pump relay wiring to see if it had the same wire cut.

 

I would think that and 81 K5 should have a mechanical fuel pump. The third wire would not be needed.

 

See if these help:







George

 

Thank you so much!

 

Appears from George's diagrams that it is only used with an actual oil pressure gauge (not a light)??

 

It shows both. Number 31 TAN is for the gauges only, while the Pink Lt Blue and Dk blue are for the one just for a light. If I'm reading it correctly.