I have a 22" Sun Tracker fishing barge and the trim tab will go down but will not go up. Any idea what the problem may be?

SOURCE: I have a 03 Sun Tracker pontoon & Merc 60 my throttle trim will lower motor but not raise it.It works fine from motor ,up & down okAlso just had voltage reg. replaced and tach stopped working .Help

Time to just go threw all the wiring. You have a boat. It's on the water or not. On the water electrolysis kicks in 1000%. On land corrosion set in. Check and clean the wire plugs, replace if necessary. Replace ground point connectors. Add wire if necessary. Just a note. When I do boats, I solder all connections and use silicone shrink wrap on the wires.