Culvert loader wiring.

I am having the same problem. Did you ever find a solution?

There are 4 post on unit.  2 for powering accessory ( from transformer) and 2 for the switch that starts and stops the operation.  Your switch should be off.  Turn on power to transformer and shed should light up.  I actually installed a second switch on the power side to turn whole unit on and off without having to turn off transformer since it powers other stuff too.  Then when power is on (shed is lit) when a car enters loader and breaks optical beam lights will flash.  Once lights flash then turn on switch to start crane.  If you wired it like instructions say but left your switch in on position it will start the second any car breaks the beam.  I think people think the switch is to power whole accessory but its just to turn on and off crane.  FYI, they made a design change so instructions don't match how it actually operates.  The shed will light up as soon as power is applied, not when the beam is broken.  If all that is same as what you did then probably the pcb board.

I had same problem with a Bethlehem culvert loader,I ordered a new board from Lionel parts and now it  works fine!!!!

Thanks for the reply but I found the error. The previous owner had installed a jumper, maybe had a TMCC device in it and the jumper was jumped to power the crane any time the bean broke the light like you said. I then found the switch blue and yellow leads were reversed on the molex plug and I moved one wire and relpaced the jumper molex on the board with the switch wires and it now works as it should. I am going to wire both the loader and unloader to an sc-2 later. Thanks SandJam!

Glad you got it working, these are the coolest operating accessory I think.  Everyone love to watch it When they come over.