Combines variable speed reel please help

You either have a bad switch or a bad ground jumper wire on the switch. The switch is a cross wired double pole double throw switch. When switch is pushed forward it connects the ground and pos wire from the center terminals, one of which is ground and the other positive, to one side of the switch outlet terminals. When toggled the other way it reverses the connections and now makes the wire that was pos before leading to the motor neg and the previous neg wire now pos. The bottom of the switch should have a X wiring pattern to it. It can be checked out with a test light by pusing the switch one way and checking for voltage then connect the test light to a pos terminal and holding the switch the same way check the other outlet wire for ground and vice versa when the switch is rocked the other way. By grounding the switch and having it work you have found the problem - it is not getting a ground in one or both switch modes.

It would of helped to know if your corn head varible still worked. You said you run new wires both ways and all the way right. I'll add a couple points to Tbrans remarks. The ground circuit is completed back at hydralic valves threw the windings and then mount to valve stud. Remove coils to clean connection to valve stud and switch coils with any other coil except for clutch coil. Using your truck battery gives little motor much more power for you are not grounding threw a coil winding. With that being said it is possible that a loose magnet in motor is causing enough drag so it works one way but not the other with combine electrics. We have replace bunches of electric motors over the years. Good luck

I went through this exact thing last spring with our N-7 combine. I gave up fixing it oem and solved it this way. Your switch is a double-pole_double-throw switch which is exactly what you need to have to do what you are doing with the truck battery. It has 6 terminals like you would need on a circuit like this but only 3 are used. The switch does not provide ground for the circuit, it only switches positive voltage to the motor. What you need to do is rewire the switch and provide a ground wire to it like you would find on a normal switching polarity circuit. You will get greater voltage differential at the motor doing this and that will fix your problem. I believe the circuit is wired this way to allow the auto reel speed option. The oem circuit grounds through coils which act as resistors which lower the voltage drop across the motor.