Change the time on the clock

Okay you off turn off the stereo with the off button and push clock, and then hold down the audio button on the top right side and then the numbers will start flashing.

I am now the proud owner of a used Pioneer DEH-1650 unit that I got at an auction for $5. At my workbench, when I applied 12VDC between the black and red wires, I found it draws 2.4 mA approx. (the red wire needs a constant 12V to hold up the memory?). However, when 12V is applied to the thicker yellow wire as well (which I think would normally be supplied with 12V via the vehicle's ignition switch), there is nothing - no clock, no display etc, and no current measured through the yellow wire. Is this wire connected to a fuse inside the unit? If so, how do I get at it?