My brother found it when going through some of the stuff I left in storage at my folks place. Don't recall too much about it but I think I had it for my 96 Impreza L for a stereo I was going to get for it. What I do recall: It has a harness plug which must plug into the stock stereo harness in the car and has about 4-6" of wire coming out of it to splice into the new stereo wiring. It isn't a Subaru part, not sure the brand. If you need more info on the part let me know and I'll ask my brother to take pictures of it (part is in MN and I am in TX). Willing to part with it for free if you have an old Impreza and are replacing the stereo with an aftermarket unit and you pick it up yourself (Andover area).
