The high pressure is not that big of an issue. Some Mitsu engines will push up to 100 on really cold idle and the oil switches will hold just fine. It is possible to blow the switch if it is a cheaper switch or a faulty one.

The other thing is if you cold started @ 82PSI, waited a few minutes and read 78 PSI, you were not at operating temp. Go drive the thing around for a while and check your operating pressure again. It will take a very very long time to get a correct operating temp pressure reading if it just sits and idles.

I would suggest you either have a faulty switch, or the wire has an issue if you have verified the actual operating temp pressure reading.