Oil pressure gauge not working

Hello, i have a 93 pontiac transport with 195,000 miles on it. I power washed under the hood about 10,000 miles ago and since then the oil pressure gauge has been pegged to the max. Ive checked the plug at the sending unit, and followed the wires but i couldnt see anything loose or shorting out or anything. Just wondering if anybody has any suggestions. The seding unit was replaced about 15,000 miles ago. This is really the least of my problems with the van, but would be kinda nice to see if i have good oil pressure. Thanks!

bump...how much and how hard are the sending units to replace on a 95 Transport 3.8L.

I suppose you have a 3.8....in any case, gauge to the max means an open circuit on the sensor side of the circuit.
www.avigex.ca/xport/instrumentpanel1.jpg
NOw check on that TAN wire that reaches the sensor (contact A on socket)
www.avigex.ca/xport/connector.jpg and connect it to the ground with a small jumper. THis should pull the gauge to ZERO.
If it does show zero, contact to sensor or sensor is open. If it says high, TAN wire is cut somewhere...most probably near the sensor onnector.
Measure resistance to ground on the sensor contact A : should read approx 0 with engine off, around 40-80 ohms with engine running.