I wouldn't go at it with a pressure washer anyway. I know it's more work but put the degrease in a spray bottle, use a small brush and hot water in a garden pump. Slow and easy. That stuff gets inside low voltage splices and connectors you'll never get it right again.
If you have a compressor there's a tool for spraying and removing degreaser. There are also are EPA issues, you don't want to doing this 50 feet from your (or my) well.

Good luck, post how it goes.