Combines 8570 rotor not reversing

I would start with the rocker switch. I have had one go bad. Selenoid would be second, but they are pretty reliable.

rocker switch seems good swithed wires and rotor turned only one way. Is the selonoid the one on the pump behind the engineIJ

I have wanted to test those wire to control speed and revers rotor pump, but have not yet. If no one can tell you what the voltage should be on the wire for revers in the next two day I will have some time to check on mine. I don't have the book here but I'm sure there is one wire for revers and 2 or 3 for forward. On the revers line I think it should have 12 volts, if 12 volts is present then suspect internal of pump, I haven't seen diagram of pump but there would have to be some kind of selonoid for revers. On selonoid you test for with ohm meter for 10 to 100 ohm from input wire to ground, if that is ok it would be mechanical.

I look at a service manul for 8780 today. From forward _ reverse swicth to rotor control module pin 4 reverse and pin 3 forward 12 volts with thresher swicth OFF. At rotor pump pin D (maybe red_white wire) with reverse swicth on 1.24+_-.13 volts, pin A is forward and C and b are ground. With plug unplug form rotor pump coils pin D to ampmeter to ground 50 milliamps. Hope this helps SWTVID

If this ever happens again before you get the system fixed, just switch the two large hoses on the rotor motor and kick the unit in forward, the rotor will run in reverse.