I just installed a Kenwood KDC258U in our xj6 using the existing 240 watt amp in the trunk. Hindsight makes it seem easy and I hope this info does so.

1. Take console arm rest top and storage out (4 screws). Lay towards rear seat.
2. Reach inside and undo two white wing nuts for the wood grain fascia for console after removing ashtray w lighter - disconnect wiring to lighter.
3.Wood grain top of console comes off by pulling, bending and sliding rearward
4. Access to radio, clock and temp control screws exposed. My tabs were mostly brokend on the left side of radio facia. I drilled and installed small "L" brackets to reinforce and restore it. I also used JB Weld Water Weld epoxy to reinforce any other plastic surface to side of new radio chassis where needed. I also adjusted the new radio bracket so radio is about 2 inches more forward than factory for easy access to small station buttons on faceplate.

Wiring from factory HK unit wiring harness:

1. 2 large brown wires on end of white radio connector are always hot. Use either one of them by either installing new radio 12V wire into the pin slot, push all the way in and super glue or silicone it to secure. Or splice into factory harness, wrap and insulate.
2. Small ignition wire next to brown wires is only hot with ignition on. Locate, install new ignition wire from new radio and secure.
3. 3 plugs in back of factory radio go to:
Antenna, amplifier in trunk (boot) and CD player. WHITE connector end must be cut off to expose + input feeds to factory amp.
Cut end, insulation and braiding about 3 inches back and strip the 5 wires.
Connect as below only the positive output wires from new stereo to this cable; the 4 negatives wires are hooked up all together to the 5th GREEN wire in amp cable.
Left front channel: Yellow wire
Right front channel: Black wire
Left rear channel: Blue wire
Right rear channel: Red wire

As stated earlier bundle all 4 negative channel wires from new unit to the GREEN signal ground wire and insulate all 5 connectors. I used small wire nuts or caps.

Hot wire to factory amp: In white factory radio connector the small Light Green wire with the Black stripe powers the power antenna and the factory amp! Plug into connector new Antenna hot wire to this connector and...

You have created sound.

If you need a new radio fascia plate other threads have stated that: Autoleads FP-14-00 from England works great $45 US
and Autoleads PC2-55-4 wiring harness which plugs directly into factory radio harness plug and to some new head units BUT apparently doesn't work on Alpine or Kenwood etc. This is why I installed wiring as describe above.

Don't forget to install the console wing nuts before the center console assembly and remember the black trim piece in front of the ashtray, ha.

Then pop a cold adult beverage and do victory lap after thanking the Big Man in the Hat for the wisdom of joining this forum.