Mine were under the hood. They should be by the drivers side headlight. What kind of vechicle are you using? I am having the same problem, but it is in both my truck and plow.

 

Its a 94 GMC Sierra 1500 with a 7 1/2' Western Unimount

 

Ah I dont know much about gm's. But the realys should be up by the head lights. They are available at napa. Just take your old one in. Do your low beams work when the plow isnt hooked up?

 

try swapping the two relays first..... that will tell you if it is a bad relay... Usually on the passenger side near the headlight is where you will find them.

 

I had the same problem last year. It was a bad relay cube. It looks fine, but inside it someplace there was a problem. Put a new one in and it worked like new. As far as locations, I find no one person puts things in the same place regardless. Good luck

 

Found it! Had to pull the grill off to access it behind the driver side headlights. The installer had the relays protected by a heavy plastic bag. I switch them both since I had them out. Works as good as new.
Thanks for the help.

 

I have a similar problem, about 2 months ago, my low beams stopped working on the truck without the plow on. I changed the low beam relay and it was fine for a few weeks. With the plow on, the plow high and lowbeams work. Then it happened again, this time I bypassed the plow harness and hooked it up back to the GM headlight plugs and have not had any issues. This past weekend, I replaced the low beam relay with a brand new relay and added the hardness back in and it still does not work. I'm not sure if I should replace the harness or I have another issue, it seems the culprit is the low beam on the harness. I have a MM1 on a 2001 Chevy Silverado, its a 6 relay harness. Any recommendation would be greatly appreciated. BTW this is not a new installation, I have had it installed since 2001. Thanks, Eric

 

I This past weekend, I replaced the low beam relay with a brand new relay and added the hardness back in and it still does not work.

There are 2 low beam relays in that harness, one for the truck low beams and one for the plow low beams. Did you replace the right one?

 

I only replaced the truck rely, maybe I should replace the plow relay too. I have the wiring schematic and that is what I'm following. I figured the plow lights works it must be the truck side. Over the weekend when I hooked up the plow harness with the new relay, it still didn't work. I was going to trace the line tonight and see if I can find a break in the line

 

This will also happen if your low beam tab breaks off in the plowside harness. They'll corrode and disappear sometimes, and for some reason, the low beam one is the most common. Problem sounds like a relay b/c it was intermediate, but just an FYI about the tab. Replacement splice in plow side harnesses are available and about $40.

 

Check to make sure that you have power on the brown wire at the relay with the lights on.