ok....
1.connector on the back of the instrument cluster can cause problems like yours that are intermittent.
2. your speedometer problem is related to #1 above, but can also be a loose or bad output speed sensor (on the transmission)
Both 1. and 2. can be caused by the body control computer also.
3. "Ghost Wipers" are an absolutely common problem on these vans. You haven't been lucky enough for them to actually come "on" by themselves yet! There is no permanent fix. It's not the body control module, the combo switch, the main computer, or the "fuse box". It's the park/home slip ring in the wiper motor. If you clean it up, it'll work for another 6 months, and go back to this same symptom. Oddly enough, if you use the wipers a lot, the contacts on the slip ring will keep themselves clean, so:
do like we all do and learn to ignore it, or spend a bunch of money to have it fixed, just to end up with the same problem again!
It's only a minor annoyance. But far better than a bad transmission!
Slantsixness