Yamaha 90 trim problem

My motor suddenly stopped trimming up from the helm. It trims up and down from the engine switch but only down from the helm. The switch is fine; I found leads under the console and reversed them to check. Pulled apart a three prong plug in the engine and tested there; power with down trim but not up. So I see to have some disconnect between the helm station and the engine. Anyone seen this or have any insight? I’ve searched but haven’t found a decent wiring diagram for this system. This is driving me crazy as I have to run to the transom to lift the motor when beaching.
thanks in advance!

The trim switch at the throttle arm has contact points. Over time these points can build up corrosion. This could be a possible cause if you've ruled out a harness conductivity issue. Pull the throttle arm off control, disassemble the arm to access the contact points and clean.