Where is the oil pressure sensor switch located on a 1991 jeep Cherokee limited 4 Liter in-line 6?

The oil pressure sensor switch on a 1991 Jeep Cherokee Limited 4 Liter in-line 6 is located on the back of the engine block, just above the oil filter. It is a single wire sensor with a 1/8 inch pipe thread. The sensor is held in place by a 17 mm wrench.