I installed a new Kenwood HU (http://www.crutchfield.com/cgi-bin/S-9ApsNhyAbG8/ProdView.asp?a=0&s=0&g=300&id=other_items&i=113KDC2019) into my '98 Mustang last night. The Rio will be plugged into the HU via a cd changer -> Aux adapter (also shown in the above link).

I was planning on splicing the rio's power cables into the HU's wire harness, but I'm wondering which cable is the actual power. I'm guessing it's "Ignition Sense", but just want to make sure before I start cuttin...

You need both power wires. The yellow "memory" wire provides the actual power. The orange "ignition sense" wire is the one that tells the stereo when to turn on and off.

Uh, that's probably not it... Most likely Ignition Sense (Orange) is the switched or ACC power (the one that changes based on the key location).

You'll want to hook the empeg Permenent Power Input (Yellow) to a Memory or V+ or 12V (probably Red or Yellow) or on the HU harness.

right.. the yellow wire is the easy part. just wondering what to connect to the other power wire.

if the "ign sens" is the same as the "switch" wire that i normally see, then that answers my question. thanks

Yes, ignition sense is the same as switched +12V (which is normally controlled by the ignition switch)

/Michael