The below is a post I saved years ago and can't verify it's accuracy so use at your own risk but anyway here is what I have:
"There are five wires coming out of the clock.
Black - Ground
Red - Constant +12V
Blue - Ignition Switch +12V, will turn on the display
Yellow - Parking lights (running lights), this connection will signal
the clock to dim the output to the appropriate level. Connect this to
one of the white wires coming out of the light switch (there are
three...just poke a pin in the wires and check the signal with a
Orange - Dash lights (dimmer voltage level), this connection will
indicate the appropriate dimmed level."
"Don't mind me. I'm just here for the alibi"