Combines header lift

First off, I presume you have a 3rd cylinderIJ I presume the "tuning screws" you are referring to are the raise and drop rate screws on the valve stack. Somewhere on the valve stack you will see a pressure test port. Put a gauge on it and try to lift the header. You should get 2500lbs of pressure roughly. I imagine your relief valve may be getting a little weak. The relief valve is mounted on a square block back by the hydraulic pump. If I remember right on 1688s, it is a cartridge-style relief that is sealed and non-adjustable. You may need a new relief valve. Good luck!

Remeove the screws that hold the auto header control and pull it out, disconnect the harness's and plug the combine harnesses into each other, thus taking the module out of the loop. If it works fine now the module is defective. We have had defective modules send 4 V to the master valve and overheat hyd systems so this could be sending a signal to the lower solenoid. Check the module, a few of the older open units survived. IF you can see transistors etc and it is not a solid sealed rectangle then moisture can cause this. These were supposed to be replaced in a campaign over a decade ago. Finally if you don't want to replace the unit disconnect the wire from the header switch to the module, I think it was an orange sep wire. And as always check the ground of the system, a bad ground can back feed into the system and give it false readings that cause weird things to happen.