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Western ultramount plow dimming lights a lot

Discussion in 'Western Plows Discussion' started by aquku, Jan 5, 2013.

  1. aquku

    aquku Member
    from 14432
    Messages: 40

    In our fleet, we just picked up an 02 GMC 2500HD with a western ultramount. We noticed that the lights dim way down when we move the plow left to right and up. We put in a new alternator, but the problem persists. It seems like at certain times the battery drains down to 12.00 when moving plow left to right. Any ideas on what to check...could it be a weak battery? Everything workds on the plow as it should.
     
  2. mishnick

    mishnick 2000 Club Member
    Messages: 2,243

    Could be a weak battery or just bad, corroded or loose connections. Check your battery terminals first. Think of the electrical system like an air compressor. The battery is the tank and the alternator is the compressor. Even when the compressor is not pumping the tank should provide lots more air than the compressor puts out. In your truck, the battery should provide hundreds of amperes of current for short bursts to power the plow motor. If you lights are dimming when the plow runs then either your motor is drawing way too much current or you just have a bottle neck (bad connection) preventing the power from getting out of the battery to feed that motor. If the motor is drawing too much power it is either a motor failure or the pump is seizing up. More likely to be to be just a bad connection though.
     
  3. snomasters

    snomasters Junior Member
    from Calgary
    Messages: 4

    same problem with a 2000 Ford F350 with a 7,6 Uni-mount plow ... draws a ton of power dims the lights first time I have had this problem... going to try a brand new battery tonight ..
     
  4. whiskeyjack

    whiskeyjack Junior Member
    Messages: 19

    I just replaced a solenoid. Before it failed completely, the lights would dim and the RPM's would drop each time I moved the joy stick. Not sure if it's related to your problem but it sure seems to have been a factor. New solenoid, no dimming, no drop in rpm's.

    I'm a newbe to plows and their problems so if I'm wrong, don't be shy about it.
     
  5. aquku

    aquku Member
    from 14432
    Messages: 40

    How did that battery turn out?
     
  6. SalNazzaro

    SalNazzaro Senior Member
    Messages: 311

    I hooked my plow up this morning again and noticed this as well, time for a new relay?
     
  7. SalNazzaro

    SalNazzaro Senior Member
    Messages: 311

    Solenoid I meant
     
  8. aquku

    aquku Member
    from 14432
    Messages: 40

    did you mean the motor relay? or the seloniods on the plow?
     
  9. mishnick

    mishnick 2000 Club Member
    Messages: 2,243

    Lets get some terminology right first.... A solenoid is a magnetic device that produces external motion. A relay is an electrical switch that uses a magnet to control electrical flow. A Chevy starter solenoid does both but since it actually pulls the starter gear into the ring gear it is considered a solenoid. On your plow there is a motor "relay" even though Western sometimes lists it as a solenoid.

    Now that we have that resolved lets talk about what happens when a relay goes bad. When a relay develops bad contacts unwanted resistance is put in the wire between the battery and the motor. Increasing resistance in a circuit reduces the current flowing in that circuit so this will not cause your light to dim. Increasing the current draw by reducing resistance will dim the lights. If your motor is shot and drawing too much power (too little resistance) then your lights would dim.

    The most common cause of dimming lights when plow is activated is a bad connection at the battery posts. Usually people move the plow when they are stopped and the engine is not spinning very fast so the alternator is not producing very much power, in turn relying on the battery to make up that shortfall. If the power from the battery can't get through to the plow then the headlights and everything else will be starved for voltage and your voltmeter will reflect the same.

    Of course if the battery itself is old and tired it will do the same thing but you usually know you have a bad battery because your truck will be hard to start.

    Try taking a voltmeter and connecting it between the battery + post and the + terminal of the motor. Initially it will show 12V because it is an open circuit and there is a 12V difference. Now get a friend to lift the plow and watch the voltage. In a perfect world it would go down to 0V but normal plows will show about one volt of difference. This is the voltage lost through the resistance in the wires, the relay and the connector at the grill. If it shows more than one volt under load then you need to start cleaning connections. Now do the same between the negative battery post and the negative terminal of the motor. Initially this will show zero because you are measuring ground to ground. Now get your buddy to lift the plow again to load the circuit. You will see a small amount of voltage. Again it should be less than one volt. If it is more then start cleaning the ground connections.
     
    Last edited: Dec 14, 2013
  10. Rumble

    Rumble Member
    Messages: 36

    Mishnick is there anyway to test the motor To check if it is drawing too much ?

    Thanks for the help.
     
  11. dieselss

    dieselss PlowSite Fanatic
    Messages: 10,975

    Amp probe.....
     
  12. mishnick

    mishnick 2000 Club Member
    Messages: 2,243

    That's right, a clamp on amp meter. U should see an initial burst up to about 80 or 100 amps and then should settle around 40 or 60 amps lifting.
     
  13. Tony350

    Tony350 Senior Member
    Messages: 546

    Where do you get a clamp on amp meter for dc power? I can only find ac ones? What do they roughly cost for one that reads high enough amperage for plows?
     
  14. mishnick

    mishnick 2000 Club Member
    Messages: 2,243

    I bought a pretty good Fluke clamp on meter that has ohms, volts etc for both AC and DC. Usually they read both. You should be able to buy one at any tool store. A cheap one will be fine, just not so accurate but give or take a couple amps is fine for what we are doing. We are not sending the plows to Mars or anything. Mine cost $200 Cdn but Fluke is a big name here. http://www.myflukestore.ca/p8237/fluke_365.php This is the one I bought just to give you an idea. The dial shows amps with a solid line over a dashed line for DC or pulsating DC current as well as the sine wave symbol for AC amps. It's good for up to 200 amps with an accuracy of + or - 0.1 amps. Lots more accurate than I need for plow motors. But its real nice because it has the removable clamp on sensor which is good for getting in tight spaces over large battery wires. Here is one from Princess auto for under $100 http://www.princessauto.com/pal/en/Electrical/Autoranging-Digital-Multimeter-with-Clamp/8344715.p
     
  15. Tony350

    Tony350 Senior Member
    Messages: 546

    Thanks a lot mishnick