RedFish said

The lower dash pads in the 68 forced the creation of the dum wheel radio.
There isn't adiquate space for a hand to turn knobs.
See the solution at DeMonDIN.
The wiiring is already there. Fused radio power and illumination are the red and orange to the factory radio. The power for the aftermarket radios memory is the yellow wire that feeds the door jamb switches. It is found in the taped harness along the bottom of the dash.
The 4 wires to rear speakers can be speaker wire. I use trailer harness wire. It's flat, easy to hide, 4 leads of different colors.

Click to expand...