How do I troubleshoot a bad oil pressure gauge?

[belfert]

So, I started my bus yesterday to bring up the air pressure so I could raise my air seat.  The oil pressure came up as per normal.  About 60 seconds later the oil pressure gauge dropped to zero and started bouncing around at the zero mark.  I immediately killed the engine.  I then went to the back and started it back there.  The rear oil pressure gauge showed normal pressure.

Any ideas how to troubleshoot this?  I'll probably check the ground first.

This is a Series 60 so I assume the DDEC would have suht it down if the oil pressure was really that low.

[Just Dallas]

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