IHEnter

I recently bought a Autometer A/F gauge with a blue backlight that is supposed to come on when the headlights are on. Instead of wiring it to the headlights i want to wire it to the dash lights so i can dim it with the dimmer. I pulled the plug out of the back of the headlight/dimmer switch and wired the gauge to the pin labled BTN but the light stays on all the time. Does anyone whose done this know either which pin powers the dash lights or where else i can tap into that power?

Rob x-7

tap into it from the stereo dimmer