A lot of mis-information here. A ground cable is NOT going to cause the persistent failure of a single gauge. In VERY rare cases, a bad ground may cause poor or inconsistent gauge initiation problems. This is RARE and the symptom would be 1 or more random gauges not initializing. If there has been 3-4 start cycle attempts and the oil pressure gauge is the only gauge not working - then you are wasting time looking at ground issues.
While it is true that the oil pressure sending unit is less expensive than the gauge - it may or may not be an inexpensive "might as well try" solution. First, the odds (based on our first hand experience) are overwhelmingly pointing to a gauge failure. We are about 6 for 6 in this department. If a shop takes the time and puts your car on a lift and removes both pans (required) to get to the sending unit, replaces the sending unit, replaces the ~3/4 quart of oil that will be lost, and then puts the pans on and buttons everything up - this is going to cost $60 for the sensor and about an hour of shop labor. An $800 gauge now becomes a $1000 gauge + the labor to replace the gauge.
Unlike the frail, piece of crap gauges that Ford/Autometer stuck us with (and who have been subsequently locked in a schoolyard finger pointing contest), oil pressure sensors have been around for years and are a few more orders of magnitude more reliable.
It's the gauge, sorry.
