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Discussion Starter · #1 ·
The solenoid on my 1998 Chevy with 9' MM1 failed last week, so I went to an auto parts store and got a replacement, made by S.A.M. It looked identical to the old one. After replacing and plowing for about a half hour, the solenoid stuck in the on position - I had to pull the motor connector cable at the grill to stop the motor. I went back and got another solenoid, thinking I'd gotten a defective part. Put the new one on and after plowing for about a half hour, it stuck on also. I disconnected the small wires to the solenoid to see if the switch would release, and it didn't. The plow seems to work fine otherwise, and I'm wondering what's going on. I went to a Fisher plow dealer and got the actual Fisher solenoid, which looks much more rugged. The Fisher dealer thought the problem could be the electric motor pulling too many amps, or maybe it could be the cab controller on the dash. He said the SAM solenoids don't have a good reputation, but should last longer than this. Any thoughts on what might be going on?
 

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Correct, you should def run OEM Fisher (Trombetta) solenoids, but sounds like you have another issue.

Have you done an amp draw test on the motor? I have seen situations where it will not let the solenoid de-energize.
Its also possible the solenoid is grounding itself.

I'd tend to rule out the controller if you unhooked the 2 small wires and it was still stuck on...
 

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I would first pull the pump's motor and inspect it. I'd be willing to bet it's corroded under the cap. Also check the grill connectors for corrosion and gunk bridging pins, the fact that it's engaging when the smaller wires are not connected suggests that power and ground are coming into contact with one another where they shouldn't.

Are you certain it's hooked up properly? Which pump setup do you have, SEHP?
 

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Discussion Starter · #4 ·
Thanks for the quick reply. I don't have an amp gauge, need to go to a shop to test the amp draw. According to the MM1 Mechanic's Guide, it says, "max motor amp draw at relief pressure, 200 amp. I assume that means the reading when you hold the controller on with plow all the way up or angled all the way. I've never had the cab control fail, but I guess anything's possible.
 

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While the motor is stuck running, unplug the controller. If the motor shuts off, it's the controller. If not, it's the solenoid. If you bought a Buyers solenoid first and it's one of the tall, skinny ones (which I assume it is if it doesn't look like the Fisher one) then it's probably the solenoid even though it was new. They have a pitifully high failure rate.

Edit: just reread the post and saw you mentioned disconnecting the small wires. As @JFon101231 said, that would rule out the controller.
 

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Thanks for the quick reply. I don't have an amp gauge, need to go to a shop to test the amp draw. According to the MM1 Mechanic's Guide, it says, "max motor amp draw at relief pressure, 200 amp. I assume that means the reading when you hold the controller on with plow all the way up or angled all the way. I've never had the cab control fail, but I guess anything's possible.
It wouldn't be the cab controller, not given your statements. Forget the amp draw test, that's a given factor at this point, the "why" is what you need to investigate, what's making it happen. Dollars to donuts it's due to corrosion, or power & ground coming into contact with one another. Which only leaves you with a few components:

1. The power harness -truck side
2. The power harness -plow side
3. The connectors for each side of the power harnesses
4. Or the pump's motor itself (check the terminal bolts and the underside of the cap.).
 

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Discussion Starter · #8 ·
Good ideas, RepoMan. It is a SEHP, and it's wired right. I bought the truck new with the plow installed in '98. I cleaned and put dielectric grease on the plow connectors the other day. The motor acts like it's running great, but I guess you have a point about moisture inside.
 

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Discussion Starter · #9 ·
Pulled the motor off and brought it inside to warm up. Couldn't tell if there was moisture at eight degrees. There's a tiny bit of moisture and dirty from years of use. I'll spray it with electric motor cleaner and put it back together with a little silicone sealer. I wonder if it should be lubricated or just put back together clean and dry?
 

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Discussion Starter · #11 ·
When I brought the motor inside to warm it up, I took it apart. The brushes look okay, thought I'd spray with electric motor cleaner and reassemble. Just wondering whether to put a couple drops of oil on the shafts when assembling.
 

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you buy a cheep part.... you get a cheep part.
 

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Good ideas, RepoMan. It is a SEHP, and it's wired right. I bought the truck new with the plow installed in '98. I cleaned and put dielectric grease on the plow connectors the other day. The motor acts like it's running great, but I guess you have a point about moisture inside.
Is this a ISO setup or Relay? Do you have 3 connectors or 2 at the grill?

Can you post a picture of the terminals on the side of the motor?
 

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Discussion Starter · #15 ·
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I haven't put on the new Fisher OEM solenoid yet, wanted to try to check as many other possible problems first.
This plow has 2 connectors at the grill, motor connector on passenger side, nearest the battery.
 

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View attachment 189386 I haven't put on the new Fisher OEM solenoid yet, wanted to try to check as many other possible problems first.
This plow has 2 connectors at the grill, motor connector on passenger side, nearest the battery.
Flip it over, no powdery residue underneath there? Positive terminal looks to be in good order, no play?
 

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Discussion Starter · #18 ·
The posts are tight. There is some black sooty powder in the lower end. I'm going to clean that out with electric motor spray. Not sure where all the flat washer type disks go, each spindle end and in between.
Wondering whether to lubricate the spindle ends or put together dry?
Household hardware Gas Auto part Machine Gear
 

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Discussion Starter · #19 ·
Just wanted to thank everyone that offered advice on what to do about my problem with motor relays sticking in the on position, and tell what is hopefully the end of the story. I took apart and cleaned the pump motor, drained the fluid and cleaned the reservoir and the pump filter and filled with synthetic plow fluid. I bench-tested the cab controller as per the mechanic's guide, and installed the new OEM Fisher relay switch. One thing I didn't do is get the motor's amp draw tested, and I'd like to do that. But I've done two plowings and so far so good. Still have my fingers crossed hoping for no more problems.
 

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If the motor solenoid is stuck it can be checked with a DVOM.

Those pump motors are prety inexpensive so any wear or if your having to push the up button more than once to get the plow all the way up it may be time to replace.
 
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