Here's the ideas that I started with:

Thanks to "cjuetten" for the write-up and pics from the thread DIY FACTORY FOGS shown below that show the disassembly of the fuse box and the location of the pins. The owners manual does show where the fuse (#53) and the relay (#54) install into the under-hood fuse box but his photo is worth the 1,000 words written in the manual.

https://www.chevyhhr.net/forums/how-tutorial-library-21/do-yourself-factory-fogs-637/

Green: GROUND for Relay
Purple: 12v INPUT from Fuse
Red: 12v OUTPUT to fogs
White: 12v SIGNAL from Dash switch or from parking lights. Your choice here.

The 2009 LS I have did not come with a relay, fuse or switch for fog lights. It does have the in-dash wiring for the fog light switch but this goes to the BCM. I chose not to use this. I wanted my fogs to be independent of everything except key-on power. I found some HHR OEM fog lights on Ebay. The fog light relay is GM part number 19-116057 but I found an AC-Delco relay (D1786C) at my local parts house. I chose to use an in-dash mini toggle switch with a blue LED indicator light. My HHR is blue. I also chose to use the under-hood fuse and relay ports for a neat and clean install.

I removed my waterfall and disconnected all the plugs.
I took the assembly to the workbench and laid it down on a soft towel.
I took a cut-off wheel and removed the factory fog light switch mounting bracket on the back side of the waterfall.
There is no pop-out plug for the factory fog light switch so I drilled a hole for my switch.
I soldered wires onto my switch and sealed them with heat shrink and installed my switch onto the waterfall.
I installed the waterfall after running my wires down the center of the consol.
I found a fused ignition-on circuit from the consol fuse box and ran one wire there.
The other wire got ran through the firewall to the WHITE pin shown above.
Then I ran a hot wire from the RED pin to each fog light.
If you take your time it's pretty basic.

Actually, you could use this circuit to power most any lights.
Just don't overload the relay.

 

I'm working on installing fogs in my 2010. I've checked voltages and what you've found works well but for me it does not turn the fogs off when I hit the high beams. Any ideas on a connection point that would work with low beams only?

Thanks!

 

How is your circuit wired?

 

Haven't done any wiring yet. I would like to set it up so that the fogs only turn on with low beams and turn off with high beams, much like factory. I might wind up using a second relay tied to the low beam headlight wire to enable-disable the fogs but I would prefer to find an existing contact point somewhere.

 

Splice into the low beam triggered relay harness. It would work exactly as you want, however, your DRLs would trigger the Fogs. You can disable DRLs.