You can do it with tap connectors and a line converter without doing any damage to the harness. You can even pull tap connectors back off is you mess with them enough, although it may leave some wiring exposed where they broke the insulation, to make the connection. Just run to any auto parts store and grab a pack of these:
Head to any car audio retailer, or even some auto parts stores and grab one of these:
Wire the power like you would any other amp. You'll need a diagram, to find the remote/antenna lead from the stereo. Typically it's a blue wire, and you could probably find it with a multimeter, in the absence of a diagram. It can be tapped in the same manner as for the speaker wires. Once you have that, you're good to go.
Linear Mode
