# Fisher MM1 - Plow Drops When Headlights are Turned On



## Mitragorz (Oct 11, 2013)

I just picked up a MM1. Got it for a great price, couldn't turn it down.

Hooked it up at the guys house, everything worked except the pass side high beam and pass side parking lights/turn signal.

Made a stop on the way home, turned the headlights on when I got back in, and the plow dropped.

I'll also note that on the drive there, I turned the lights on and nothing happened.

Plow works fine with the headlights off. Wound up lifting the plow and short chaining it.

https://youtu.be/LPfewcI5eGw
It's too dark to work on it now, and I'll be out of town tomorrow. First step is cleaning the grounds.

But has anyone seen this before?


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## cwren2472 (Aug 15, 2014)

It means that the 9 pin plug is bad and shorting internally on either the truck or plow


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## Western1 (Dec 4, 2008)

Yes. Guessing there is short in the harness or plug connector


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## cwren2472 (Aug 15, 2014)

Pin 1 is the valve to lower, adjacent to pin 2 for the low beam


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## Randall Ave (Oct 29, 2014)

Use the Fisher/Western replacement end, better quality than the aftermarket ones.


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## Western1 (Dec 4, 2008)

Had a customer that said when he turned plow lights on the plow would drop. It was a toggle switch set up for the lights. Sure enough that’s what was happening!!!


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## Mitragorz (Oct 11, 2013)

Sounds like I’ll replace the plow side plug. I actually replaced both the truck side and the plow side on another MM1 that I already had. The parking lights weren’t working, and it wound up being the truck side plug.

Easy peasy.


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## Randall Ave (Oct 29, 2014)

Western1 said:


> Had a customer that said when he turned plow lights on the plow would drop. It was a toggle switch set up for the lights. Sure enough that's what was happening!!!


Multiplexing systems new features.


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## Randall Ave (Oct 29, 2014)

When you put the plow in float, does the light come on?


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## cwren2472 (Aug 15, 2014)

Mitragorz said:


> Sounds like I'll replace the plow side plug. I actually replaced both the truck side and the plow side on another MM1 that I already had. The parking lights weren't working, and it wound up being the truck side plug.
> 
> Easy peasy.


You may be able to determine it by holding 1 end rigid and manipulating the other end where it enters the molded plug. If not, you got a 50/50 shot anyway

Edit: and what @Western1 said below


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## Western1 (Dec 4, 2008)

Keep your toes clear!!!


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## Western1 (Dec 4, 2008)

I have a video of it but can’t figure out how to post it.


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## cwren2472 (Aug 15, 2014)

Western1 said:


> Keep your toes clear!!!


Oh, yeah, I probably shoulda added that


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## Randall Ave (Oct 29, 2014)

Western1 said:


> Keep your toes clear!!!


Darn gravity.


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## Mitragorz (Oct 11, 2013)

Randall Ave said:


> When you put the plow in float, does the light come on?


When it's acting up no, I don't think it goes into float. But I'll check again.


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## Mitragorz (Oct 11, 2013)

Randall Ave said:


> When you put the plow in float, does the light come on?


It DOES go into float. The float light comes on, and the light in the controller goes back to green and stays green as long as it's in float. Take it out of float and it's flashing red again.

https://youtu.be/2RNzOZR6xeU


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## Randall Ave (Oct 29, 2014)

When you turn on the lights, the plow drops. When you put the plow in float, does that light come on?


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## Mitragorz (Oct 11, 2013)

Which light are you asking about?


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## Randall Ave (Oct 29, 2014)

I thought you stated, when I turn on the lights, the plow drops?


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## Mitragorz (Oct 11, 2013)

When I turn the headlights on, the plow drops (free falls) without me touching anything. All the lights work (minus the pass side high beam and parking lights.). Truck headlights are off, plow lights are on as normal. Everything about that is fine, it’s just when I turn on the headlights, the plow drops down. The controller is flashing double red.

It doesn’t go straight into float mode when it falls, but I can put it into float mode like I normally would, by holding the down button. When it’s in float mode, the float light is on and the red flashing button goes back to green, and seems to stay green as long as it’s in float. When I take it out of float, it goes back to flashing double red.

I think I covered all the lights!

In the video in my first post you can see the plow drop as soon as I turn on the headlights.


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## H3lzsn1p3r (Nov 23, 2020)

If im not mistaken the controller is flashing double red because the lights turning on is back feeding the controller i have seen the plugs cause this so id take a visual look at the plow side plug and truck side see if there is anything visually wrong.... another thing you can do is test the pins on the truck side with a test light put your plow lights on and see if the down solenoid pin has power to it with the controller not in float, if no power at the pin then id be looking at replacing the plow side plug


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## Mitragorz (Oct 11, 2013)

H3lzsn1p3r said:


> If im not mistaken the controller is flashing double red because the lights turning on is back feeding the controller i have seen the plugs cause this so id take a visual look at the plow side plug and truck side see if there is anything visually wrong.... another thing you can do is test the pins on the truck side with a test light put your plow lights on and see if the down solenoid pin has power to it with the controller not in float, if no power at the pin then id be looking at replacing the plow side plug


The truck side plug is brand new, I just spliced it in maybe a week and a half ago. I have another MM1 that it works fine with, but testing the pins takes no time at all so I'll do it anyway. Though I'm pretty confident it's the plow side that's a problem. Already have a new plug on the way.

Pin 1 on a 9-pin is down, correct?


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## H3lzsn1p3r (Nov 23, 2020)

Mitragorz said:


> The truck side plug is brand new, I just spliced it in maybe a week and a half ago. I have another MM1 that it works fine with, but testing the pins takes no time at all so I'll do it anyway. Though I'm pretty confident it's the plow side that's a problem. Already have a new plug on the way.
> 
> Pin 1 on a 9-pin is down, correct?


Should be


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## cwren2472 (Aug 15, 2014)

H3lzsn1p3r said:


> If im not mistaken the controller is flashing double red because the lights turning on is back feeding the controller i have seen the plugs cause this so id take a visual look at the plow side plug and truck side see if there is anything visually wrong.... another thing you can do is test the pins on the truck side with a test light put your plow lights on and see if the down solenoid pin has power to it with the controller not in float, if no power at the pin then id be looking at replacing the plow side plug


So, you are suggesting that it might be a bad plug? Do you have, I dunno, a schematic of the plug pin out you can post, perhaps?


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## Hydromaster (Jun 11, 2018)

cwren2472 said:


> It means that the 9 pin plug is bad and shorting internally on either the truck or plow





cwren2472 said:


> So, you are suggesting that it might be a bad plug? Do you have, I dunno, a schematic of the plug pin out you can post, perhaps?


Lol


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## Mitragorz (Oct 11, 2013)

I didn’t do any formal testing, but when I was unhooking them plow this morning I did notice that the headlights come on when I drop the plow. And they stay on in float, so it does look like the down circuit and the headlight circuit are shorting together.


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## cwren2472 (Aug 15, 2014)

Mitragorz said:


> I didn't do any formal testing, but when I was unhooking them plow this morning I did notice that the headlights come on when I drop the plow. And they stay on in float, so it does look like the down circuit and the headlight circuit are shorting together.


You should look into that bad plug that @H3lzsn1p3r mentioned. I think he could be on to something...


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## Randall Ave (Oct 29, 2014)

Mitragorz said:


> I didn't do any formal testing, but when I was unhooking them plow this morning I did notice that the headlights come on when I drop the plow. And they stay on in float, so it does look like the down circuit and the headlight circuit are shorting together.


That's what I meant. If your truck side plow is new, I would replace the plow side plug. You could pin it out with an Ohm Meter if you're game.


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## Mitragorz (Oct 11, 2013)

cwren2472 said:


> You should look into that bad plug that @H3lzsn1p3r mentioned. I think he could be on to something...





Randall Ave said:


> That's what I meant. If your truck side plow is new, I would replace the plow side plug. You could pin it out with an Ohm Meter if you're game.


Yeah, the new plug came in yesterday. I'll get to it in the next few days. No snow in the forecast unfortunately...


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## Mitragorz (Oct 11, 2013)

New plug solved all the problems.


Thumbs Up


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## Western1 (Dec 4, 2008)

Glad to here that. Good luck!


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## Mitragorz (Oct 11, 2013)

Ok, so as it turns out, it's NOT fixed. And it's definitely truckside, as I hooked the truck up to another plow, same plow I've been using for almost a decade, and it's giving me the same grief.

As soon as I turn on the headlights, the plow falls. Parking lights are fine, high beams are fine... But as soon as the low beams come on, that's when I see the issue.

I've tested both plugs on both plows and they're fine. I can jump the low beams (pin 11) and ground (pin 5) right to the battery, and I get no feedback with a test light on any other pin. So it's not backfeeding through the plow side. Something in the truck is commanding the plow down when the low beams come on.

I replaced the relays today. No change. I had used generic 5-pin relays, and those have given me issues in the past, so I got the real-life Western part (the line at my Fisher dealer was out the door into the parking lot, in the rain).

I also picked up a new Western branded truck side plug, even though I replaced the truck side plug about a month ago. It's pouring outside right now and I don't have a covered space to work, so I'll splice that in tomorrow.

In the meantime, what can I look at on the truck side to troubleshoot, in case it's not the plug and just crossed wires somewhere?

The plow works fine with the lights off. Works fine with high beams or just parking lights. Low beams are the problem.

EDIT: The handheld controller I have flashes double red as I mentioned before. It also flashes double red when the plow is DISCONNECTED and the controller is on (and headlights either ON or OFF). Not sure if that's normal or not, I never noticed, but something worth noting I think.

It's not a Fisher or Western handheld, it's one of those generic SAM controllers, but I did hook up two old school joysticks that I have laying around and I had the same problem. AS soon as I plug in the joystick, I hear clicking inside the controller when the headlights are turned on.


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## Western1 (Dec 4, 2008)

Not really sure about what’s going on but the drop wire is white with a yellow tracer and low beam is black. I’ve crossed the white and the white with yellow tracer before but doubt you crossed the black with the white/yellow tracer. So I would think some where they are touching.


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## Western1 (Dec 4, 2008)

They are next to each other in the grill plug so I would be looking there. Or at the relays if some work was done there?


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## Mitragorz (Oct 11, 2013)

Everything seems OK at the relays. Everything is connected to the correct pins per the diagram, and I get good continuity on the black and white wires from the relay to the plug.

Unless I'm wrong, the only place where the two wires would even come close is in the harness, after the light wires dive into the sheath. Coming out of the sheath, the control wires are separated by their own sheath.

Here. Plug is off to the left, lighting wires are exposed, control wires continue on in their own little sheath off to the right.










I'm hoping that it's the plug itself, but my fear is that there's chafing further up the chain, between the plug and the spot in the photo. Not the end of the world to rewire it, but still...


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## Western1 (Dec 4, 2008)

Most likely in the plug


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## Western1 (Dec 4, 2008)

Try unplugging and turning low beams on then check for power at grill plug on post 1 and 2. Guessing there will be power on both


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## Mitragorz (Oct 11, 2013)

Western1 said:


> Try unplugging and turning low beams on then check for power at grill plug on post 1 and 2. Guessing there will be power on both


Great minds. I actually just came in from doing that.

With the headlights on, if I jump Pin 5 to ground (to energize the relays and tranfer power to the plow lights) Pin 1 is energized:









It's a little tough to see, but PIn 5 is jumped and the test light is in Pin 1

Pin 2 is also energized, as it should be.

I think what I'm going to do next is pull the low beam terminal off the relay, manually put power to it and see what happens with Pin 1

EDIT: Just did that. Nothing on in the truck, key off, light switch off, I hotwired the Black low beam wire directly from the loom to the battery, bypassing the relay. Sure enough, that energized Pins 1 and 2.

To me that's the nail in the coffin. The only question is if it's the plug or chafing somewhere in that sheath. I guess I'll find out tomorrow.


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## Western1 (Dec 4, 2008)

Ok keep your toes clear


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## cwren2472 (Aug 15, 2014)

Has anyone asked @H3lzsn1p3r for his input?


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## Mitragorz (Oct 11, 2013)

New truck side plug cured all.


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## Western1 (Dec 4, 2008)

Glad to hear!!! Good luck!!!


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