A friend who has a boat with an old Mercury "tower of power" 150 horse
outboard is having a problem.

When the motor is in neutral, it will tilt up and down as it should.
However, once put in gear and moving forward, the motor will only trim
down, but not up.

The motor has had a new (rebuilt?) trim pump installed, and the wiring
harness was replaced. This work was done to get it running and back
in the water after having been stored for years. The problem surfaced
when lake testing for the first time.

Is there some kind of lockout/limit switch that operates when the
motor is in gear that could be causing the problem? Only thing I can
think of is the helm control could have an intermittant connection in
the "up" switch circuit that quits when the control is moved to the
forward gear position.

Any advice or experience?