Metra 70-8901 1990-2005 Subaru Into Car Wire Harness
I remember when I was but a lad (back in the 80s) and was cutting and hacking the wiring harness to hookup radios, and this little gem saved both the car and my personal agrivation.  Easy and well marked fit was perfect and the company shipped immediately.  If you buy a stereo get the wire harness.  it's a great and inexpensive time saver.