Land Rover Repair: 97 Discovery losses power

Question
97 Discovery losses power when ac switch is turned on after washing engine, runs good when ac is off,does the ac switch need to be replaced or something else.

Answer
My guess is that water got into one or more of the electrical connectors under the hood.  I'd suggest blowing them out with compressed air, making sure that are clean, and putting in a little dielectric grease prior to reassembly.  Cleaning up (drying out) the connections should do it, if the problem is truly a consequence of engine washing.