Or use a jumper with a light bulb in the middle. Jump the positive to negative leads after removing from battery.

 

Late to the conversation, and don't have the electrical background you all seem to have, but have fried an oil gauge before realizing the reason the original one was bad was because the sending unit was incorrect. Short version, wrecked my 28yr old 1993 pickup, bought a used '95 out of CA with "different mileage that records showed". Seems they swapped in an upgraded gauge cluster without changing out the idiot light oil pressure sending unit. The sending unit tested correctly for resistance, so thought the issue was the gauge, pulled the good one out of my '93 and promptly fried it. Started doing some research and figured it was the sending unit, ordered the correct one, lucked into a salvage yard '94 pickup with the correct cluster and swapped out the speedometer (with odometer) portion, which was just a few screws as I recall (being SUPER cautious opening the gauge housing). And all worked as it should. Now if I could just figure out what's draining the battery...but that's for another day. I don't know if oil pressure gauge are electronically different (resistance settings, or whatever - not an experienced electronics guy), from different models, mine came out of another truck. I have since found gauge clusters from a '97 T100 and a '90 4Runner and want to either remove the oil pressure receiver to replace the one removed from the '93 pickup, or upgrade the clusters in my son's 1999 Tacoma or the wife's 2002 4Runner. Just don't know if the corresponding oil sending unit needs to match the source of the oil pressure gauge, or if the gauges are the same, but the sending units must match the vehicle in question (and be for gauge not light). Either way, hesitant to try anything and fry another gauge. So far though, things from the same model have been fairly straight forward swap ins, with some upgrades from similar year 4Runners.

 

The correct OEM oil pressure sending unit, 83520-34010, was about $70 from Toyota of San Bernardino. Went over it several times to be sure it wasn't the sending unit for the oil light. This was for the '95 pickup, and the gauge cluster came from a '94, both with 22RE 4cyl motors. Swapping out the speedometers with the odometer was straightforward, hardest (most nerve racking part) was opening the housing.