Reverse goes forward

I use a friend's boat on the Santee Cooper system, last time down the 1990 force 125hp motor started acting up. While fishing we were leaving and I put the boat in forward and it started going backwards, after a little bit of pulling on the cables, the boat started going forwards in forwards and reverse in reverse. I think he has messed with the cables because to crank the boat in neutral the handle is not quite in the neutral setting. Anyway, the next morning when we tried to go out, I put the boat in reverse and it would pull straight forwards up on the bank. Ended up not going out, becasue that is the wrong lake for something bad to happen to your motor. I live 4 hours away, so I am trying to trouble shoot what to repair before I go back. Any suggestions? thanks for any help you can give. bk

Must be a fault in the control box. maybe the gear arm is coming loose? could possibly be the locking bearing to clicks it into neutral position has played up, so the arm rotates more freely. i'm not too sure to be honest, bit of a weird fault. I'd say it would be the control box though and not the gearbox.

Also make sure the control lever is not coming loose, i had problems, could get it to go sometimes and felt strange to use.

Take the shifter off the boat.Un-hook at the motor.Make sure the motor is shifting ok.Try to move it in and out of gear while it's turned off.Shift into forward and then reverse all the time turning the prop.That checks out ok,then make sure it's in neutral.
The shifter.Make sure it;s unhooked from the motor.Then shift it back and forth.All the while looking at the shifter.No loose parts??That ok put it in neutral.Then hook it back up to the motor adjusting the connectors on the cable to make them fit.J