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Unimount MVP. Where do I start?

Discussion in 'Western Plows Discussion' started by bsayles, Oct 17, 2010.

  1. bsayles

    bsayles Junior Member
    Messages: 11

    I bought an 8.5 MVP Unimount with 12 wire plug. It has a 6 button control pendant (hand held control). I have the motor relay wired up how the directions say. I have also tried a couple of different variations of wiring it. The relay that came with the wiring looked terrible so I went to Advance and got a aftermarket relay. According to the wiring directions for the MVP, the brown w/ red to the small right terminal, brown w/ green to the small left terminal, orange w/ black to negative battery terminal. The wiring diagram shows the positive lead from the battery to go to the farthest large post from the small terminals on the solenoid, but the new relay says the lead from the battery goes to the large post closest to the small terminals. Does it matter? My main question is, how does the relay work? Once 12v is applied to the one of the small poles it creates a circuit and closes the contact on the relay to the large posts powering the plow motor? Thats how every relay I know of works. With this wiring set up, inside the pendant, the 12v red wire from the ignition switch connects to the brown w/ green wire. Now that brown w/ green wire goes to the small left pole on the relay with 12 volts to it. The brown w/ red wire I'm assuming is from the power switch on the pendant going to the right small terminal. Now if you have 12v going to each of the small leads on the motor relay, you have a stalemate of electricity on each pole and a circuit is not being completed without a ground. I could be wrong. I hope I am. How does it work? By the way, when I push the power button on the pendant, the power signal led comes on.
    Beyond all of that, skip why the power isn't bridging to provide power to the plow motor. As soon as I bridge the terminals on the solenoid, the right wing on the plow pulls in and continues to try to pull in until the bridge is removed. Why is that? Bad circuit board in the pendant? Not a short. I have checked and wiggled wires all along the harness. I guess with all of the questions I'm asking it is difficult to answer, but where do you think I should start? I've checked for shorts between pins and shorts to ground. I did find a broken wire to S6 solenoid on the plow. The pins looked terrible, so I cleaned both plugs up. The no 12 pin on the plow side broke. It was hanging on by a thread. Ordered a repair harness. waiting... waiting... waiting...
    Any suggestions would be appreciated. Thank you!
     
  2. bsayles

    bsayles Junior Member
    Messages: 11

    Another question I have is, can I replace the 6 button control pendant that I have with a 9 button control pendant as long as both have the 10 pin set up?
     
  3. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The old 12 pin MVP's are unlike other plows where everything is grounded and then controlled via a 12V input, instead they're constant hot and then controlled via the ground side. This includes both the hydro solenoids on the pump as well as the under hood motor relay.

    So the brown/green is keyed 12V, the brown/red is the ground trigger to trip the relay. Completely backward from most others.

    Good chance you also have the incorrect relay if you purchased from an auto parts store unless it was specifically package as a snowplow solenoid. Can't use an automotive starter solenoid as neither of the small terminals are a ground. One is 12V (obviously) and the other is also 12V but only when the relay is tripped. No grounds there.

    Terminal locations on the under hood relay do not matter as long as you have the correct relay to begin with.
     
  4. bsayles

    bsayles Junior Member
    Messages: 11

    It is a relay for a western plow not for a starter or anything. I did check the voltages coming from the brown w/ red when different control inputs were made and the voltages were continuously changing. Why though is there never any power at the terminal going to the plow? Is there a different relay for the MVP and other western plows?
     
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Use an actual test light, not a DVOM. Check the brown/green for 12V first which probably but more critically check the brown/red for good ground. If the test light is nice and bright then the new relay is defective...which is very common if it's an aftermarket.

    You can also use a ground jumper to trip the relay by touching it to the same post as the brown/red is on. If the relay doesn't click and the pump motor doesn't run then either the relay is defective or you battery cables/connections aren't good.
     
  6. bsayles

    bsayles Junior Member
    Messages: 11

    Brown green has 12v, but where does the brown red ground? The schematic shows it just goes between the controler and the relay. WHere is it supposed to ground to?
     
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The controller (thus the relay when it's triggered) is supplied ground through the orange/black wire. And the orange/black should be terminated directly to the negative battery terminal.
     
  8. bsayles

    bsayles Junior Member
    Messages: 11

    the relay clicks when I ground out the brown red terminal on the relay to the negativ battery terminal. I don't understand. I'm sorry. Where do I go now? By the way there is still 0 volts at the large terminal that gose to the plow when I bridge the brown red to the ground. Also does it matter which large terminal the power cable from the battery and the power cable to the plow motor goes to?
     
    Last edited: Oct 17, 2010
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    For starters the relay is likely defective if you're sure your positive cable from the battery to the relay is good. Because once it clicks you should have full battery voltage on the other large terminal.

    Then what about the orange/black? Do you have it directly on the negative battery terminal? If so and there's still no ground trigger on the brown/red then either the wire is broken on the harness, it's pin has an issue in the control plug, or the controller is defective. If you've been moving wiring all around trying different ways before you asked for help there's a good chance you blew one or both of the internal fuses in the controller. Have to disassemble the controller and check them if you need to go that far.
     
    Last edited: Oct 17, 2010
  10. bsayles

    bsayles Junior Member
    Messages: 11

    Yes, even when the relay clicks, there is no voltage on the other terminal. Does it matter which terminal either power cables are on? Also, how do I check the relays in the control? What am I looking for there? The orange black is directly connected to the negatrive battery terminal. The ground is good also. I have checked every ground in the system and everything is good. I think that the control was hosed when I got it though too. Brown/red wire has good continuity back to the cab connector with no shorts to ground or to other wires.
     
    Last edited: Oct 17, 2010
  11. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Makes no difference which one is where as I stated before. So replace the relay but this time purchase a good one or you'll be going through this again...expect it'll be in the middle of a storm when you need it the most. Search "Trombetta" here.

    Remove the screws and separate the halves of the controller and you'll see the two small fuses on the board. Check them both for continuity with a DVOM.

    Be sure to disconnect the controller from the truck before you disassemble it.
     
  12. bsayles

    bsayles Junior Member
    Messages: 11

    One fuse has no resistance and the other has 5.05 K ohms so obviously blew that one. Where do I get fuses that small? Sorry didn't see the doesn't matter which pole before. I do really appreciate your help.
     
  13. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Try an electronics shop first and if no luck head to the local Western dealer but be ready for sticker shock.
     
  14. bsayles

    bsayles Junior Member
    Messages: 11

    Ok. Obviuosly there is not going to be anything open right now, being Sunday night. Advance up here closes at 7 on Sundays so I can't replace the relay tonight. I will also buy a western relay for a back-up. I hope that everything works out when I put the new fuse in the control and the new relay in. I really really thank you for your help. If this doesn't all fix it, I hope that you can help me again. Thank you!
     
  15. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Happy to help and once you have the fresh parts just give a shout if you need more help. We're here all season. :D