Oil pressure w/ engine off!

'78 Ford F250 (460). Put the key in and turn the power on without turning the engine on and the oil pressure gauge goes halfway up - right in the middle of the “normal” range. Start the truck, and the gauge goes almost to H (high).

So the question is- is this more likely to be the sending unit? Or a problem with the calibration of the dash gauge?

If it is a problem with the gauge itself, is there a way to reset it?

Start with the sending unit. It should be easy to locate, pull off the connector and reattach. If no change price a new unit and replace it if the cost is reasonable.

I don’t think there are ways to recalibrate the guage. If the sending unit is OK have the pressure checked by a mechanic with his guage. Likely the only was to repair the guage is remove and replace the entire guage cluster in the instrument panel.

Unplug the sending unit and turn the key on. If the gauge stays at zero, then your problem is the sending unit. If the gauge still moves to half way, then the problem is the dash gauge.