1996 B190 Speedometer/Stalling Problems

[rubyslippers6232]

We haven't been able to take our van on a trip since the beginning of the year because of problems. Chassis is a Ford E350. Speedometer needle flips wildly and has been doing this for a while. Didn't matter whether we were going uphill or down, or flat. It was ok because it was still driveable (although not real comforting). Then it started cutting out when we would idle, especially (but not only) after rain. Our mechanic has replaced the computer, among many other things, and thinks it may be a wire that is getting wet, but can't find which one, and says it's like finding a needle in a haystack. We are all so frustrated. If anyone has any suggestions, please feel free to suggest. Big trips in the van were replaced by trips in our Ford Focus, 2-3 people plus a large dog. We need our van!!!