the oil pressure gauge pegs over to the high end when the engine is running. on 1994 Isuzu Rodeo

The gauge reacts immediately like there is a short somewhere. How do I determine if the problem is the gauge or the engine sensor?

Asked by for the 1994 Isuzu Rodeo
DOES IT PEG WITH KEY ON ENG OFF?
The gauge only pegs when the engine is running.