Rover Curious is absolutely right. Your going to fry the factory amp. Even with a lower powered after market deck (18x4).
Also, Are you sure the deck you are trying to install is truly a double din ? There are din and a half decks (1.5's) on the market that will fit much better into a D2.

 

i would love to put a double din in my disco but its a lot of work to make it fit

 

OK for your radio problem you have 2 options the first option is to either get an amp integrator (Best Buy has these for about $30 if I remember correctly and walmart has one for less) or to cut some RCA's and plug the plugs in to your aftermarket radio and wire the cut ends to your factory harness (what plugged into the factory deck) (thats kind of the cheap hack way of doing this) The better choice would be option 2 and rewire the whole system (relax its not as bad as it sounds) buy a spool of speaker wire from walmart (16 or 18AWG is fine) and find the outputs from the factory amp. then basically use your new speaker wire to connect your aftermarket radio high level outputs (white,grey,purple, and green wires) to the amp speaker output wires (I used the rave cd to find out what color these wires are) you can also use a multimeter to test the resistance on these wires your speakers should read around 8 or 4 ohms and a "AA" battery to "pop" the speakers but I wouldn't suggest that unless you know what you are doing. Mobile audio is what I do for a living so I will be happy to offer any more detailed help you may need. I can also probably tell you what you need to look for and where to find it.

 

I had to wire Constant power (Yellow wire) from my ignition switch (or fuse box) to the radio (make sure you put a fuse on that wire right at the ignition switch (or fuse box).

 

I am also very interested in seeing some pics of your custom dash mod. I am going to be making a fiberglass sub enclosure where one of my jump seats go for a single 12" sub very soon so I will put up pics of the whole build incase any one is interested.

 

i am very interested not only the double din dash and also the sub box ur planning on building we have been talking with a co worker about doing sum fiberglass boxes at work and that was one of my ideas

 

i'm going to look for the amp integrator first, but i'm not opposed to the rewire. could you tell me what the colors are since i don't have the rave cd...and its too damn cold here to be messing around with it all day!! i got the wiring harness from crutchfield, and they didn't include anything about the amp, which i thought was wierd. i've been doing stereos for a while on the side, but never had to deal with factory amps! i've never been a fan of them and would love to get rid of it altogether someday.
the amp integrator....so i wire that to the leads going to the amp then use the rca's on the back of the radio and its done?

 

My rave CD does not list the disco 2's so amp bypass would be tough to explain without seeing the truck. but the stock amp is most likely some where in the passenger kick panel area (up high on the side wall) the size of it is about 5 or 6 inches square by about 2 or 3 inches thick and would have heat sink fins on it like an aftermarket amp, the wires on it can be identified by matching the smaller wires (at least most of them) to the wires behind the deck and the larger wires going to the speakers will be in twisted pairs may have to cut back any tape around all the wires to see them twisted together, there should be 4 twisted pairs mine are all black wires with different color stripes (blk\brn,blk\yell,blk\wht,blk\red,blk\blu,etc.,etc .) but they should be the heavier wires. hope this helps for now.

 

metra makes the amp integration harness for your truck it is 70-1786 this harness will require front and rear rca outputs to work otherwise you will need the scosch (cheapest and just as good as any other)converter from walmart (car audio section,it is a small light blue box). The scosche converter may be your best bet anyways since you already have a harness (just wire the converter inline)

 

i'll check there in the morning. i looked online and they say it isn't an instore item, but i do remember seeing them before. i wish we had a quality stereo shop around here!!
about the constant wire...the harness i got supposedly works with a freelander, and it mentioned something about reversing the red and yellow wires, i tried it both ways, and reversing them let everything work and keep settings on the deck. all of this makes me sound like a novice, but i really do have experience, must be out of practice!! or is the rover just a different animal??