Looking for a ground wire

I would also not recommend using the furnace T stat wires for 12V ground as the "ground" you find there goes through the furnace control board and will no longer be at ground potential when the T stat calls for heat.

That's an interesting comment. I'll have to test this when I get back into it in a few weeks. We shove off tomorrow morning so I'll have to use the new LED strip at full brightness until I can install a dimmer.

My low side dimmer requires access to the LED to ground wire, which I can't easily access from inside. I ordered 2 of the dimmers Doug pointed to. If I can't use that outside I'll have to get a high side driver to make a high side dimmer. That 1 part costs $6 so that's almost a deal breaker right there. I usually design around parts I have on hand.