I have a 1996 115 HP mercury outboard. About 1 year ago I heard a humming noise with the boat parked in my yard. It was the tilt trim motor running in the up position, to it's stop, and trying to continue. I had to disconnect the battery for it to stop. During troubleshooting I disconnected 2 of the 3 tilt trim switches (the one in front at the trolling motor station and the one on the engine). After reconnecting the battery the tilt trim motor still tried to raise the motor. I did not try to disconnect the switch on the throttle lever. I ordered and installed both tilt trim relays, new items. Solved the problem for 8 or 10 boat trips. Then, while running on the lake, the engine trimmed all the way up. I could not get it to go down. I disconnected the battery so the trim motor would not continue to run. Pulled over to the bank with my trolling motor. After an hour or so, reconnected the battery, and the trim worked correctly - for about 1 hour, when it trimmed all the way up again. Perhaps the newly installed relay failed again in the closed position? Seems unlikely. Any ideas?