Tunze Water Level Controller 5017 problem..?help

[JPotter]

I have a salt water tank with a Tunze water level controller. It has a high water sensor with alarm and water level sensor. If the water level is OK the sensor tip is in the water and the green level light is on. When the water level drops and the sensor is not touching the water the green light goes out, a low level light comes on and the pump is activated. When the water reaches the level sensor the green light comes on and the pump stops.

This is what happens now:

The high water sensor works fine..sensor, light and alarm tone
The water level sensor works in that when the water level is adequate the green light is on, when low the green light is off

BUT when low the red light and the pump do not come on.
The LFS I got it from suggested I replace the pump. I did..with a direct wire to wire connection (not a crimp box) and no go..no pump on and no red light.

Is this something I can fix within the black box itself? The box is mounted high on a wall not adjacent to the tank..it doesn't get wet.

It seems a shame to ditch a system that has working sensors...I just have to figure out how to activate the pump.

Thanks for any help.