To start with you have the Oil pressure gauge connected to an Oil Pressure relief valve and not the oil pressure port. I tried doing that and it didn't seem right so I went out and got my Oil pressure gauge from Arlen Ness Motorcycles back in 12/29/2008, he sent me a kit that attaches to the rear Valve cover, where it is easy to see the gauge as you ride. The kit included a Y connector block that attached to the oil port and allows you to install both the Light pressure switch and the mechanical oil pressure switch. I don't know if his son is still in business or not Arlene Ness died some time ago. I paid $192.99 for the bolt on kit switch, breaded hose and Y block to attach both pressure switches the Kit Part # is 15-666 and their number is or was 925-479-6350, www,Alreneness.com 6050 Dublin Blvd., Dublin CA. 94568. I don't know if that is your problem or not but it seems like it could be. Hope that helps.
Carlos