Have you looked in the trunk to see if it was pre-wired for a changer? You might get lucky.

Running the cable to the trunk isn't too difficult. On my 850 the factory or perhaps the dealer installed the cable down the right side of the car. The trim comes off rather easily allowing one to tuck the cable in under the carpet. The fold-down rear seats further simplfy things. You don't want to run the cable right through there though. Grab the top of the side bolster of the seat (the part that doesn't fold down) and pull. It pops right out and will reveal a nice way through to the trunk.

In my car the changer was attached to the underside of the parcel shelf via a couple of L-brackets and four screws. Check up there for a pair of wires, one with an in-line fuse. Mine are green and black and provide power to the changer.

-Will
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854 - 244 - Mini

I mounted mine in the glove box. I removed the screws holding in the glovebox, drilled a small hole for the cord and changer mounting bracket. Its a very easy install. I didn't want to try to run the cord back to the trunk and I like that I don't have to get out of the car to reload the changer. I used the power off the glove box light. Mine is an alpine with aftermarket cord so it works fine with the head unit. You lose some space but I was only keeping the insurance card in the glovebox anyways. Good luck.