# Plow Light Problem



## Gary M (Feb 19, 2017)

Hi Everyone
I am new to this site and I have a wiring problem that has me stumped. I have a 2008 Chevy 2500hd with a 8.5' Fisher V plow that I have owned and operated for approx 4 years now. The plow has never giving me any problems until now. My right side low beam on the plow quit working. I checked bulb and that was good,checked socket that bulb plugs into and I have power to low beam post. The low beam is working on left side and high beam is working on both. Do I have a ground problem or should I be looking deeper into the wiring?


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## dieselss (Jan 3, 2008)

What lights do you have. 2 bulbs low and high?


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## Gary M (Feb 19, 2017)

No one single halogen h13 bulb


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## dieselss (Jan 3, 2008)

Ok if it uses one bulb and shares the ground then it can't be the ground as you say the high beams work.
But you said you had power at the low beam pin? Correct?


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## Gary M (Feb 19, 2017)

Yes, that is what is confusing me.


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## dieselss (Jan 3, 2008)

Then if you have power, you need to see how much.
Did you try switching bulbs or trying a new one


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## Gary M (Feb 19, 2017)

Yes both I switched bulbs after I already purchased a new one. I have a multimeter and I will check the voltage. I was only using a test light to see if I have power. I will compare Left side to Right side to make sure I have the same voltage. Also I print the wiring diagram from Fisher's site. I will also check voltage at the harness on the truck for the low beams. Thank you for the idea.


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## dieselss (Jan 3, 2008)

While using the meter, use the test light as well so your loading the circuit. Also do the same to the negative circuit as well since your there.


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## Gary M (Feb 19, 2017)

Hi just came back in checked lights on plow while hooked to truck. Truck not running rt side low beam is showing 11.3 volts & left side is showing 11.7 volts. Truck running both side showing 14.3 volts. I checked low beam post and ground post at light bulb socket. So I am getting power to bulb socket. I guess I will keep trying maybe check all connection still thinking bad ground, but I do have high beam so can not be that. Starting to get a headache from thinking about this may have to take a break. Weather is going to be nice the next week so I will not need plow for a little bit.


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## Gary M (Feb 19, 2017)

So I came in from tracing wires back to module. Every is clean and connected. When I was out there I checked wiring at bulb socket and noticed that when I turn on high beam that the low beam post on right side still had power? Not so on the left side (working side). I am starting to wonder if the truck harness coming from module has a short. Tried grounding out harness to energize it but can't. I would like to check #1 post for power. I believe that is the post that goes to low beam right side?


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## Gary M (Feb 19, 2017)

Was able to energize truck harness and my voltage with truck not running for both right and left side is 11.8 volts could i be looking at a bad bulb socket?


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## dieselss (Jan 3, 2008)

This is odd. 
Some trucks will turn on the low with the high so I'm leaning towards normal.
Your voltages seem fine so that's out.
Did you check the ground voltage by chance?
Is this the rectangular lights by chance?


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## Randall Ave (Oct 29, 2014)

Sounds to me like he has a bad ground circuit, then its back feeding, that's why he had current at that other circuit. How did you check your grounds?


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## dieselss (Jan 3, 2008)

That's whats confusing. Single ground, and one works and one doesn't. And I'm betting the high beam isn't dim ither


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## Randall Ave (Oct 29, 2014)

Yah, well I have for you I haven't looked at yet, Its a friends truck. 1995 ford f-250, 7.3 Starts runs, then stalls. He removes the small wire from the alternator, it runs fine. Not the battery wire, but the plug in wires. Cant type, darn dog.


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## Randall Ave (Oct 29, 2014)

Don't mean to hijack the thread.


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## dieselss (Jan 3, 2008)

That should be the excitation wire and the diode wire. Tells the alt when to turn on.
When unplugged does it still charge?


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## Randall Ave (Oct 29, 2014)

dieselss said:


> That should be the excitation wire and the diode wire. Tells the alt when to turn on.
> When unplugged does it still charge?


I don't no as I havn't looked at it yet. With that unplugged it should not charge, I think, not sure.


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## dieselss (Jan 3, 2008)

Correct, should not charge.


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## Gary M (Feb 19, 2017)

Dieselss My lights are the oval ones and as I stated the left side that is working when checking bulb socket on high beams there is no power to low beam post. Tomorrow I am going to bypass plow harness with a couple of jumper wires to see if I can get light to work. That way I can tell if it is the plow light harness or the truck harness that is the problem. Not sure how to check the ground circuit but i did check for voltage on the bulb socket ground post there was a small amount of voltage 0.4 volts. I will also be checking the ground post on the truck harness tomorrow for any voltage. Thanks Dieselss and Randall Ave for your input it is giving me some direction to go on.


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## dieselss (Jan 3, 2008)

Try this .....


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## boutch (Aug 3, 2015)

Hi Gary. I just got the same problem as you are describing today. But mine is a Dodge but have H13 plugs also. I metered the fisher 3 pin connector at the head light to the module plug and I got a short between ground and high beam. With power to the head light I had voltage but around 11 volt when connected to fisher harness and 13 volt from the OEM plug. I beet you got a short like me in the fisher H13 male plug.


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## Gary M (Feb 19, 2017)

Hi Boutch I thought the same thing and replaced the plug yesterday. That didn't help but i do believe it is a short. Hopefully in the plow light harness and not the truck harness or the module. I was just heading out the door to try bypassing the plow harness by jumping from the truck harness directly to the right side low beam plug.


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## boutch (Aug 3, 2015)

Hi Gary, I would stop looking for voltage from the fisher harness, a bad ground or a weak short could give you a voltage reading with a miltimeter but notting will work when you have an electrical load on. unplug the fisher harness from the truck OEM plug and meter the low beam pin from either end for continuty and check for shorts beteewn low beam pin to the others pins at the other end plug. Did you try pluging the truck head light back to the OEM harness to see if it was a truck side problem or fisher wiring problem. good luck


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## Gary M (Feb 19, 2017)

Morning Boutch I just tried to jumping the plow harness that did not work so i plugged back to truck disconnected ground at bulb plug and grounded bulb plug to truck ground. Got very dim low beam now on right side and good low beam on left which was not causing me any problems. So i am going to try your idea of a continuty test but on the low beam wire from module and while i am in there i will also check ground.


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## Gary M (Feb 19, 2017)

Ha Dieselss or Boutch I am tracing the wires back to the module. It is a 3 port module and the port the controls lights is port "A" and wired into the harnessfor lights is a relay. Could it be possible that the relay is bad? I did a continuty test from relay to harness plug on both ground and low beam wire and both tested good also is there any way to check module with meter?


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## boutch (Aug 3, 2015)

On my dodge the head light are on plug C. Should be the same on chev


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## boutch (Aug 3, 2015)

Sorry, you are troubling shooting power out to the plow lights. Start trouble shooting from where power come from on the truck connector to fisher harness and plug A on the module.


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## Gary M (Feb 19, 2017)

No on my chevy it is Port "A" I just went out to double check.I have never heard of a relay only going half bad. I checked wire feeding relay and the wire going out to truck plug all is good. If not relay then it has to be module. Hate guessing wish I knew for sure. that module is $177 on fisher site. Hate to change that and it is not the problem so I am going to get a relay first (cheaper option). Problem is it is a fisher part and the local auto store does not have a match for it. The nears fisher dealer is 40 miles away. So everything is on hold until i get this relay. Thank god the weather looks great for this week. Thanks again


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## boutch (Aug 3, 2015)

Ya sorry. Plug A is power out but plug C is power into the module. Is power in all good


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## Gary M (Feb 19, 2017)

Not sure i am going out to check now but my truck light are fine. Just got off phone with local Fisher dealer and that relay is not avaiable i would need whole harness. So much for cheap opition.


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## boutch (Aug 3, 2015)

Oops. A little miss communication. All that time I thought you were looking at power to the module. That where my problem was. From the truck power to the module port C, I got a short in the connector connecting to the OEM head light plug.


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## boutch (Aug 3, 2015)

Ya if you unplug the plow from the truck and your truck lights are all good. Power to the module is good


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## Gary M (Feb 19, 2017)

Boutch you might be on the right track i found a wire feed low beam on port C that look like it has worn a little need to see if i can pull wire and pin from plug because it is up tight to plug if i can get pin out of plug and reattach wire just maybe it is the problem be back with you in a little while.


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## Gary M (Feb 19, 2017)

Well Boutch that was not the problem. The wire had a little rubbing on it but was not all the way thru. Tape it up and position the module so no more rubbing. I still think it is that relay which can not be bought need to buy the whole harness. I checked every wire for power leading to the module Port C and did a continuity test on all wires in the harness everything is checking out fine. Maybe if i beg a little the dealer will allow me to plug in the new harness and if that is not it return it for a refund. Be worth trying. Thank you again for your help and i will keep you updated. Taking a few days off this headache.


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## Randall Ave (Oct 29, 2014)

When you get time. With you plow connected. Per the wiring diagram posted. Remove the plug from the module. Run power to the pin in the connector, and run a direct ground at the connector. This should tell you if that circuit is good.


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## dieselss (Jan 3, 2008)

Did you ohm out the wire through out the system


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## Gary M (Feb 19, 2017)

First Randall Ave If i do what you suggested i need to figure out how to power that relay because once i unplug from module there is no power to relay and the circuit will stop at the relay. I thought about jumping relay but got tired of working on it. When i unplug relay my truck lights come back on so i need to figure out how to trick the module into thinking the relay is still there when unplugged?
Dieselss No i didn't ohm out the wire. This is all new to me I am neither a mechanic nor electrician so i am learning on the go. Next time i get to it i will try that. What should i be looking for as far as ohm's goes in the wire? It takes a little work to get to the module it is buried behind the right side headlight and i need to take grill out then the headlight assemble to get to it.


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## dieselss (Jan 3, 2008)

Unplug the bulb.....test low beam pin to plowside pin, (lowest number is what your looking for).
Then plug in the plug and go from the socket to the plug at the iso.


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## Randall Ave (Oct 29, 2014)

Diesels, what relay is he referring to? I haven't seen it in the wiring diagrams.


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## dieselss (Jan 3, 2008)

Randall Ave said:


> Diesels, what relay is he referring to? I haven't seen it in the wiring diagrams.


I saw one in the diagram....I'll see if I can dig it up


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## dieselss (Jan 3, 2008)

Found it...


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## Randall Ave (Oct 29, 2014)

That's simple enough. He has to check for power out. And he can run battery to the wire out to the head lamp to see if it works, and it should tell him if the circuit is good.


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## boutch (Aug 3, 2015)

What about taking the adapter and relay out. Then check if he as low beam with out it.


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## Randall Ave (Oct 29, 2014)

All he has to do is jump current to the supply side of the relay, see what he has out there. Also, is there power and ground at the relays? And these are common relays. Any good auto parts store should have them.


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## Roz17 (Feb 14, 2017)

Since he has these adapters installed, I assume that the Chevy has a 4 headlamp system and the plow has the 2 light system. Can you swap the left and right headlamp adapters? If you can, and it is a bad relay/adapter, the low beam that is out should swap sides and when you test the voltage on the low beam post of the bulb socket with high beams on, the voltage should be seen on the opposite side as before. My guess is that these relays use the truckside high/low beam voltage as a signal and then switches another 12V source to feed the appropriate posts within the socket of the 2 bulb system. Just a guess.


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## Gary M (Feb 19, 2017)

The plow is a 2013 and the relay is just one big relay. Fisher has now updated it to two relays as shown in that second diagram. Already checked my local NAPA store and they do need carry that size relay fisher only part. I would like to jump relay but when i unplug relay my truck lights come back on so i think i will also need to ground out the plug for relay so module kicks power out to plow harness and then run two jumper wires on plug to right side headlight ( blk/wh wire = power and blk wire = common) to see if the circuit is good or if it is the module that is causing the problem


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## Gary M (Feb 19, 2017)

Morning everyone, I am going back at it again today. I just jump the relay and low and behold I have lights. So it looks like it is that relay, what makes me mad is now I will have to get the whole truck harness (approx $170) for a $15 relay.I have been looking to see if I could get an aftermarket relay but can not find one that is remotely similar. The relay as I stated before is one big one and has 6 pins, power in and out for both side low beams, Ground and a Common. I am heading out shortly while I have truck tore apart to get new harness. I will report back later with hopefully some good news.


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## Gary M (Feb 19, 2017)

Well Everyone I want to thank you for your advice. It ended up being that relay as I suspected. Everything is back to normal now with a new harness on the truck and $160 less in my pocket. Again Thank you everyone


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## dieselss (Jan 3, 2008)

Glad it's fixed......sucks it's so expensive


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## Randall Ave (Oct 29, 2014)

Gary M said:


> Morning everyone, I am going back at it again today. I just jump the relay and low and behold I have lights. So it looks like it is that relay, what makes me mad is now I will have to get the whole truck harness (approx $170) for a $15 relay.I have been looking to see if I could get an aftermarket relay but can not find one that is remotely similar. The relay as I stated before is one big one and has 6 pins, power in and out for both side low beams, Ground and a Common. I am heading out shortly while I have truck tore apart to get new harness. I will report back later with hopefully some good news.


Post a picture of the relay, kind of curious what it looks like. Glad it's fixed, unfortunately nothing is cheap anymore.


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## Gary M (Feb 19, 2017)

Hi Randall Ave here is the photo of the relay it is 3 1/4" x 1"x 1" and has 6 pins. The new harness has two relays which look more like a typical auto headlight relay. I questioned the dealer why does it need a relay at all. The relay is for the low beams only way does the low beams have to have them and not high beams? Again thank you guys for your help.


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## RWS81 (Dec 6, 2014)

where is that relay located?


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## Gary M (Feb 19, 2017)

Hi RWS81 this was a problem I had last year and the relay was located on my truck up by the modulator which was mounted behind right side headlight. Had to take grill and headlight assembly out to replace the wiring harness. As stated in my post the new harness comes with a two relay system instead of the one relay pictured above. Hopefully next time if the problem arises again i can get just the relay. Hope this helps


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