I pretty much ruined my young engine (214K miles). Here's what happened.
I'm not a professional, and please excuse me if I do not use the correct terms. As I understand it, there are three types of oil sensors: An electric oil switch for a dummy light An electric oil sensor (sending unit) for an SR5 gauge. An aftermarket mechanical oil gauge
I drive a 1989 Toyota Pickup dlx. The dash HAD the standard oil dummy light. Toyota had the goofiest design for this electric oil switch. This switch used a single wire to the wiring harness. With this design an open circuit kept the oil light in the dash in the off (unlit) position. Conversely, a closed circuit illuminated the dummy light if the oil pressure dropped below Toyota's pre-determined pressure. In a perfect world, this system works. However, the design of the little wire clip to the oil switch is a "push on / pull off" style. So if the wire works loose from driving off road, your light will not alert you. There is nothing to notify you if your oil switch doesn't operate properly.
For $120 I purchased a lifetime alignment for my truck. Since I was in for an alignment, I had them change my oil also. I think they may have bumped the wire loose, but I have no way of really knowing it. It was only a couple of weeks later when my engine made so much noise in such a short period of time, but the oil light did not illuminate. I parked it and checked it out immediately. I also cut open the oil filter and found it full of metal shards. The metal plugged up some of the oil channels and burned up a few rocker arms and overheated part of the block. That was apparent when I removed some of the head bolts. I found that the wire had indeed become unplugged - the light came on.
It would have been better if an open circuit would illuminate the light and a closed circuit would keep the light off. This way if the wire was loose or cut, you would know.
The only thing that would have helped me is to look at all of the lights on the dash as I turned the key to the on position before starting the engine. The oil light should illuminate before starting the engine. Make this a habit. I missed this very important detail.
I have since put in a new engine and also put in an SR5 instrument cluster with a new oil sending unit on the block.