This probably won't help you, but it's a funny story regardless.
This summer my nephew and I took my 1975 Newport 28 over to a local marina for haulout and bottom washing. The guys were waiting for us to pull up into the slip, lifted us right up and got to work, and we were back in the water in a half-hour or so.
However, when I turned on the depth sounder before leaving, it was dead -- nada, nothing. I went back to the guys and told them what was happening, and if they could think of any way the power washing could have damaged it.
They had no ideas, but they volunteered to pull us up again so I could have a look at the hull to see if anything had come loose, or whatever. This they did -- for no extra charge -- and nothing did we find. I resigned myself to a pricey fix, and when they dropped me back in my nephew went below to check it again as I was tipping them an extra $20 for their trouble.
He came up with a big grin on his face and told us all, "It's working now! I just wiggled the wires on it and it came right up." All of us looked around at one another, rolled our eyes and had a good laugh.
I thought it was GREAT of them to offer to lift us again to have a look, without asking for more money. I will definitely go back to them for more work when necessary.
So, have you tried "wiggling your wires" yet?