I have an 05 Sierra that did not come with fogs from the factory. I am trying to add some aftermarket fog lights and having issues. the stock wiring harness has provisions for fogs and terminates in that location. After installing a new fog switch and relay and verified fuse is good I am not getting power at the ends of the fog harness. I can hear the relay clicking so I know it is working to that point. my question is since my truck didn't come with factory fogs does the harness need to be attached to the under side of the relay plug ? I have some stuff attached to the fuse box so it is a PITA to take the cover off and I don't want to unless it is absolutely necessary. Thanks

 

Does the dash indicator light come on? Did it have the harness that terminates at the lights themselves? Is there 12V at the purple wires going to the lights? Are the lights grounded?

 

The fog switch illuminates when pressed. The relay clicks. The stock harness terminates at the fog locations and the harness ends have plugs to seal the ends. There is no 12v at the harness end

 

I'm going to be adding fogs to a 05 Silverado CC. It is my understanding that the wiring from the switch to the fuse box is already there and just need to add the correct switch and the relay. I do not have any wiring from the fuse box to where the lights will go and will have to add it and pin the green connector under the fuse box as shown here. Perhaps you can check your green connector for the proper wiring and also the harness ground.

 

My 05 didnt come with fog lights, all the wiring was there, all I had to do was add a factory switch inside the truck

 

Same with my '06 SS; just had to add the switch and foglights of course.. but at first they still wouldn't light up. Years of the connectors just hanging there had oxidized the pins enough that they weren't making a connection. Several rounds of spraying them with DeOxit and "working" the pins (plug/unplug/repeat) and now they work 100%.

Richard