I changed motors and rebuilt the new one. My oil pressure sensor is stuck in a fitting on my old motor so I went to the local salvage yard to get one and now when I went to start cranking till I got oil pressure it doesn't light. I took the black plastic sheet off the cluster and it lights but very dim. I did change lights. Also I plugged it into the old plug and it didn't light at all. Could it be because I used thread sealer and painted the block? any ideas?

It is not a sensor - it is a switch. Basically, just an on-off function based on pressure (think Hobbs switch). It is possible to have high resistance because of a bad connection to the block.

If you ground the connector for the switch directly to the chassis or battery, does the light turn on? If so there is your answer.

Well it was ground. I use chanalocks (spelled wrong I beleive) to get the old sensor out of my fitting. I wrapped a good wire around the threads of the switch and then wrapped the other on the ground wire from body to intake manifold and plugged the switch in and the light was glowing like the rest of them. I used gasola which is like a paste that seals very good and I think it cut the ground off of it.