Sounds like your tilt/trim relay is bad. It's inside the engine cowling. If you hear a click when you try and trim, it is the solenoid in the relay trying to power the trim motor, but probably corrosion due to arcing of the relay contacts over time has built up enough so current doesn't pass through to the motor. Can try repeated actuation, sometimes the repetition will physically break through the layer of corrosion and it will start working. If that don't work, you can try hotwiring around the relay, but be careful. Disconnect the battery, unwire the relay and hook ground to one of the motor leads coming to the relay and hot to the other. Hook up the battery and the motor should trim up or down. Reverse the leads to the motor and it should go down or up. If it does, change the relay.
Mike, April 2010