On normally aspirated cars the power steering pump may not have to be removed to access the oil pressure sending unit. On turbocharged cars and normally aspirated 944s that have added external oil coolers, the addition of oil lines for the external oil cooler provides additional obstruction that requires the power steering pump be moved out of the way to access the oil pressure sending unit.

Disconnect the power steering pump (leaving all lines attached) and hang it out of the way. Remove the belt tension adjusting turnbuckle without changing the adjustment and you will be able to reinstall the pump without having to adjust the belt.
Disconnect the two wire leads to the oil pressure sending unit (located just below the oil filter).
NOTE
When you replace the unit, you should use a new crush washer on the sender. The Porsche PET nor the 944 Parts and Technical Reference Catalog show a crush washer on the sending unit. However, on every car I've ever replaced the sending unit, there was a crush washer. So, go to your local auto parts store and get an M18 x 24 (the important part is the M18) aluminum or copper crush washer.

Using a 15/16" or 24mm stubby open end wrench, loosen the oil pressure sending unit. Have some catch rags in place to catch any oil that drips out. Also, have the new sending unit ready to install to minimize the amount of oil that drips out.
Remove the old sending unit and immediately insert the new one. Torque the sending unit to 35 Nm (25 ft-lbs). This will require a 24 mm (15/16") open ended crow's foot for your torque wrench. If you don't have one and don't want to go buy one, just make sure the sending unit is snug but, don't force it or you'll damage the seal ring. As long as you use a new seal ring, it shouldn't leak.
Reconnect the wires to the terminals of the new sending unit.