How does the cluster's oil pressure gauge work?

Stock sending unit is right above the oil filter.

More than likely, the original owner just unscrewed the stock sender and installed the autometer's sender in it's place.

A TEE will give you two ports so you can install both, but more then likely you might need to buy a new OEM sender since yours might be MIA.

The plug is a simple 1 wire push on type of plug that should be hanging in the area