03 silverado remote wire from head unit

i have a 2003 silverado and i do not have a 12v remote wire on my wiring harness of the stock stereo... i have one that puts out .2-.3 Volts when the head unit is on, but that's not enough to turn on a relay... i hooked it up, and i can't get anything out of it... i really don't want to mount a switch for the amp, is there any way i can make my stock head unit turn on my amp?

it's a true story... the radio is triggered on by what's called "the class 2 databus system" i normally run remote wires to a fused accessory circuit in the fusebox.