Headlight out on truck and plow

[Danielbean]

Hey guys looking for some help. Drivers side headlight was working on and off (would stay on for a few days and then out for a few days) that went on for about 2-3 months now it is completely out. When I plug the plow in, the plow headlight is out also, also when I plug it in I can hear and feel the relay switch clicking don't think that is normal. Changed both relay switches and no difference. I have a 4 port isolation mod and when I unplug #4(passenger side) and plug into #3 pass side still works, same in reverse when I try to plug driver side into #4 it does not work. Any suggestions would be greatly appreciated. Thanks in advance.