Problems: Head unit doesn't work w/o headlights??

[Project240]

OK, I've got a pretty weird problem. We just got done wiring the speakers in my 240 (Infinity Reference 4x6 component plates in the front, Reference 5.25" component system in the back, subs/amp to follow), and the Pioneer head unit as well. It works, but here's the thing: with the ignition on, the main power lead to the head unit only shows 9 volts on the multimeter instead of the necessary 12, and the head unit won't come on, just blinks this weird pattern (presumably because it's not getting enough power).

BUT, if you turn on the running lights or headlights, the multimeter will suddenly jump up to 12 volts on the main power lead, and the head unit works great. Turn the lights off, and the head unit cuts back out and goes back to 9 volts.

.......WHAT the f***.

[nab911]

Check your head unit wiring unless its a direct plug. Either you power (HU side) is hooked to the illumination wire. See if adjusting your interior light dimmer changes anything.

[sidewaySilvia]

I would definitely associate it to head unit wiring harness.. Might have your amp turn on and main power hooked to wrong things in ignition harness ... Does your head unit come on when key is in accessory position?