Is it 11V DC though? Some newer cars (e.g. VW) have a PWM signal for dimmer since the signal passed to the stereo is more than just on off. i.e. the dash brightness control also controls the brightness of the factory stereo's backlighting. The empeg doesn't have this. It simply has an on/off setting.

If you've measured it with a multimeter on DC a switching signal it could quite rightly measure 11V. A poor man's check for a switching signal is to put the multimeter on AC volts. If it reads non-zero then it's likely it's a pulsing signal.