'94 mercury tracker pro series 60 trim won't go down

when i use trim, going up always works, going down only works sometimes i've tried the switches on the motor, throttle and the bow all with the same results? the wiring from the motor to the trim motor is cracked up in areas and wire is exposed with some green coloring to the copper wire could this be it? like is said though the trim tilts up fine. this is my first boat so everything is new to me. any help would be greatly appreciated. the wire from the motor goes directly into a metal cap on top of the trim motor two phillips screws hold the metal cap in can i take this cap off and change the wire or will this break the seal and allow water in the trim motor. i know a lot of questions..... sorry. just want to get this trim problem taken care of, want to go crabbin this weekend on the bush river

thanks, harry


boat is a

1994 pro deep v tracker 17'
mercury tracker pro series 60hp