I've got a 2003 discovery ii with the Nav system rather than the stock radio. I'm looking to replace it with a kenwood radio that I already have from a previous vehicle. the problem is the wiring is completely different. the kenwood uses a 16-pin plug which is completely different from the 3 plugs that go into the stock radio. and also the antennae wire plug in is different on both as well. anyone know of the correct harness or wiring adapter to purchase for this? Or am I just going to have to take it to a car audio shop? I'd rather do it myself if possible.

 

You can do the change yourself if you want. First of all how many rca outputs are there on the kenwood stereo, second, how many antenna cables do you have going into your oem nav unit, not counting the gps antenna(there should be two, a large diameter and a smaller diameter one). Once you know this, you will know what wiring harness you will need. Also, if you have the rear headphone amp(behind the back seats) and want them to be functional(they will only have volume controls). Get back with this info and i can give you info on what you will need. While I do not have the nav unit, i did the changeover with the High Line Alpine unit.

 

I'm not worried about the rear headphone thing working, just want all the speakers to work. and if possible and not overly complicated, the steering wheel controls. the head unit I have is the kenwood excelon kdc-x397, it had rca inputs labeled front and back and then another set for subs. and I believe there are 2 antennae wires going in to the nav system. one bigger and one smaller. as you can probably tell I'm rather new to car audio but I'm learning.

 

that is all the info i need.
You will need the metra 70-1758, You will not use the rca connectors, the metro connector with the rca connectors is not compatible with the nav units. I checked with Crutchfield, and the nav use different connector than the non-nav units.
Metra 70-1758 Receiver Wiring Harness Connect a car stereo in select 1986-2005 European vehicles at Crutchfield.com
for steering wheel control, you need the PAC SWI-RC unit, and since your kenwood does not have the 3.5mm remote input for remote control, you will use the wire instead(I downloaded the manual of your kenwood and it is straight forward) I found a used one on eBay for 18.00 and it worked great. I have all the instructions to install and can email to you.
PAC SWI-RC Steering Wheel Control Adapter Connects your car's steering wheel audio controls to select aftermarket car stereos at Crutchfield.com
For your antennas, they are called diversified antenna, the large one is am/fm and the smaller one is fm only. the link provided is where i got mine.
Landrover DISCOVERY 03 2003 ANTENNA ADAPTER Y SPLITTER 2 FEMALE 1 MALE
metro 89-9400 to fill in gap left by the 1 din install.
Metra 89-9400 Dash Kit Fits select 1999-2004 Land Rover Discovery models ? single-DIN radios at Crutchfield.com
I would get the metra harness, the pac swi-rc, and the kenwood harness and connect all the wires, before pulling the oem stereo. Once you have all the wires connected(I recommend solder and heat shrink), then you can pull your head unit, plug in the harness you built, and program the steering wheel controller.
I gave you links to the items, but you do not have to get from Crutchfield, you can get all on amazon, eBay or Best Buy or wherever is the cheapest.