Aux Fog lights on with low beams

14Silverado14 · August 6, 2015

2014 Silverado 1500 LT

Ok,everyone seems to want the factory fogs to come on with the high beams. I installed Hella fogs on my brush guard and want them to come on separately with only the low beams (the law here). Chevy garage will not pass for inspection if they aren't.

I don't want them to come on with the factory fog lights. I want them to come on separately. I may want the factory ones on or I may want the Hellas on or I may want both. I like options.

Problem: when the high beams are on the factory fogs go out but the low beams stay on so I can't just wire into the low beam circuit. I don't want to wire into the factory fogs or the Hellas will only come on when the factory ones do.

Been looking at diagrams and it looks like the ground disconnects from the factory fogs when the high beams are on. All I need to know is what wire and where do I tap into to run to the relay for the Hellas to only come on with the low beams and go out with the high beams.

Edited August 6, 2015 by 14Silverado14

RobZ71LM7 · August 6, 2015

What you can do is have a relay that is triggered by the low beam circuit to make your positive lead hot. A second SPDT relay, shown below, can be used to make or break the ground for these lights by tapping into the high beam circuit. Put the light's ground on the terminal 87a and your chassis ground on 30, when high beams energize this relay the ground circuit will be open (moves from 87a to 87) and your lights will go off.

Not sure if there is an easier way, but this is how I've accomplished a similar task in the past.

14Silverado14 · August 7, 2015

Can you draw me a diagram or make a terminal list. My terminology might differ from yours. I'm trying to draw this out on paper but not having much luck.

Thanks for the help so far.

14Silverado14 · August 7, 2015

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Edited August 7, 2015 by 14Silverado14

TJay74 · August 7, 2015

I would be very careful of doing this mod, all of the lighting is controlled by the BCM in this truck via the CANBUS system. That system is very sensitive to voltage changes.

Do as you like, but you can cause issues if you start tapping into circuits.

14Silverado14 · August 7, 2015

I've read this bulletin however my relay is not mechanical so this shouldn't apply if I am correct. I will make a trip to the shop and ask them. I also read something about lighted switches and was going to post it but can't seem to locate it right now.

I do appreciate the warning. I did do some reading beforehand however this project has given me tunnel vision to just get it done. You have just tapped me on the shoulder and told me to step back and look at the situation before proceeding and I do thank you.

14Silverado14 · August 13, 2015

So you are saying to use one relay to control 12v TO the fog lights and another relay to control ground to the fog lights. Am I correct ? Do I need to use 2 double throws or just one for the high beams. Checked with a Chevy mechanic and he stated there should be no problems wiring this circuit into the existing wiring.

14Silverado14 · September 8, 2015

Thought I would post some pics and an update on the fog light wiring.

As you can see from the pics I chose to add switches in the overhead console. This came before I even knew about the upfitters switches. I never though a car/truck company would have done this. After checking with GM service they gave me an OK on not having any problems or issues tapping into the low and high beam circuits. They even complimented me on a very neat and clean install afterwards.

Everything works: the aux fog lights go out when the high beams are on. The other switches are for trailer rear spot lights and bed lights. The acc switch was installed in case I wanted to wire something in later because the wiring for all this was a bit of a pain. All switches are fuse protected and ran through relays.

The extra ground wire that's hanging isn't needed but I left it in there for future use. It's all a tight fit but it all goes in there. There's plenty of room above the headliner for the relays and fuse holders. I did not need to drop the headliner, I just fed them into the open space. All power came directly from the battery.