Forget messing with the controller... for now. The likely cause of the problem is the trim limit switch located on the gimbal ring (port side) on the outdrive. If the switch or wires fail your trim up will not work but trailer will. Go into the stern of your boat near the transom and locate 2 black wires that go into two connectors, one with two blue/white wires and one with a purple/white wire (should have 12V when trim up switch is pressed). Pull the black wires out and jumper between the two connectors. Try the trim switch, if it works the problem is your trim limit switch or wiring. If not your control switch or wiring may be the problem.
Been there LOL. The black wires should come through the transom just above the driveshaft behind the engine. The wires are only a few feet long so the connectors should be there someplace. There are two pairs of wires, one goes to the trim gauge, the other to the trim limit. Good luck on finding a skinny kid.
Turns out, it was indeed the trim limit switch. Question now is, seeing this switch works by the position the two halves are in relation to each other, why does this switch even need to be mounted on the drive? Don't want to pull this boat out, just for that.