Mike,
You need to provide a little more information to get accurate advice.
Remove the "Crown" cover on the rear of the counterweight and post what system it has. (IE...EV1, EV 100).
You could also post the serial number, but some do not have access to the panel / serial data and its better imo to just look when posting on a forum.
The early generations were not very tolerant of water and gets wet very easy especially when washing off the battery without removing it from the truck.
You may get lucky by unplugging the battery, removing the card, and blow it dry inside. Then leave a fan on the panel to dry it completely. In my experience it is a slim chance of success but worth trying.
On the older units, if the panel trips, it will not close the directional contactors until you reset it by disconnecting/reconnecting the battery. I have to assume you have already performed this several times.
Most times the control card gets damaged from being wet and having the battery connected and may require replacement.
If it doesn't operate after drying off, I would suggest calling the local dealer, or a competent independent shop. Be sure to ask for a tech with experience in the older unit such as yours.
If he is competent, he can diagnose the issue as either an input to the panel, or an output from the panel with just a few voltage checks on the card itself.
If the card has been damaged and needs replaced, it will need to be programmed for you particular unit.