Ditto what everyone else said. I would add: Install your new gauge in an unused port under the oil filter. That way you can compare actual oil pressure with what the light does. The only negative to this idea is that it will be on the unfiltered side of the oil pump (naturally higher pressure), however unless your filter is really plugged, the difference won't be all that great.
Having said all of that, there COULD be another tapping on the LH side of the block where a turbo would be fed from on a 7610. If you find another plug exactly in line with the existing sensor, use that one.
Oil pressure issues on those tractors are RARE. I would suspect faulty wiring or a swapped bulb as the others have already said.