Checking electric oil pressure gauge

I have a 78 SB with electric oil pressure gauge.  It does not read correct pressure.  Is there a way to check the gauge without just replacing it?

I installed a new oil pressure sending unit with no change on electric gauge.  Checked engine oil pressure with a mechanical gauge as suggested on another posting.  Readings are 30 at idle and up to 40 psi at 40 mph.  Looks good.

The electric gauge reads 20 when driving or not driving, with engine running or power turned off and reading does not change with change in engine rpm.  When unpluged from sending unit, and engine off, it reads 45psi and while still disconnected from sending unit and with key turned to accessories the needle pegs at max.

Thanks in advance for any ideas or suggestions.

Wil, you might have a problem with the printed circuit board, on the back of the gauge panel. They are known to delaminate, and have corrosion on the terminals. Check to see if the connector(s) is plugged in well, and there is not funky green stuff growing on any of the terminals.
Those gauges also should have a resistor/shunt on the backs of them, for calibration purposes. there may be problem with that.

Thanks Adam.  I checked the connection at the pressure sensor and it looks ok.  Now I'm having trouble getting the center gauge bezel out to check the gauge.  Found two screws on top, one on each side and removed the nuts holding the radio in but can't find any screws on bottom.  Must the center consol be removed to get access to additional screws or is the gauge bezel just wedged down behind the center consol?

There are 2 threaded studs that go into the console from the gauge cluster. You may be able to reach those through the back once you remove the side trim. Should be a 7/16 nut on them. Another way, you have to remove the shifter plate and go in from there. Either way you need to be a bit of a contortionist. Be careful not to force anything on the cluster, they're pretty easy to break. My 68 is a pot metal part and very brittle.