I just bought a 1986 chevy 1/2 ton with a fisher plow. I hooked up the plow and it won't go up or down, or left or right. The controls work, if I move the pistons on the valve body it still does'nt work. There is no load on the pump. it turns free, and is full of fluid. The truck has sat in a garge for the last three years and has not plowed. I think the up/down piston is stuck too.

Maybe a relay , do you have a isolation module under the hood ? Do you know what this is ? Or a solenoid that directs the hydraulic oil for that .

2002 Fisher Minute Mount Inst-Act Wont Angle [Archive] - PlowSite ...

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Nov 17, 2011 - 90 posts - ‎9 authors
My plow went up it was jerking and did it in steps , but , it got there . Now , it onlyjerks when i try to angle it right or left or up . I filled the fluid ... Drop it and if it doesn'traise you can just use a jack and shorten the transport chain to hold it. .... I do havecontinuity on the plow side for all 3 wires going to the plug . Hooking Up A Fisher Minute Mount 2 In Under 1 ...
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Most of those systems don't have a driven retraction on the piston. It is gravity feed back. There is a valve that is sticking or out of adjustment. http://library.fisherplows.com/?cat=38

If you have a Minit Mount two it's probably the valve sticking. It's electronically controlled so if it clicks, then the solenoid is working and the shuttle in the valve is stuck. Can be disassembled and cleaned. New ones are best but pricey.

Have a 2004 hmm and plow went up and down but jerked left to right but did not turn , found it to be wire harness going thru fire wall , sheet metal wore thru wires shorting them out , pulled harness thru and shrink rapped and hooked back up been working fine.

check the wiring connections on the plow solenoids to be sure they are correct, the second step is check the controller box, using a continuity check via multimeter set for DC voltage. I have an old western plow that had similar symptoms, and was the controller box.

does the pressure release close to raise the plow?

I have the same problem, I do see the power light come on when I hit the key to start the truck but it goes out when I let off the key. If I park it in the garage with the furnace on it stars working and is fine until I don't won it for a day or two then its dead again. No idea why control is dead or sitting in garage with the heat on gest it working.