You certainly don't use the rear fog light relay. All the instructions are included in the kit, and they are quite good. The only difficult step is cutting the holes in the bumper airdam trim. Volvo recommends removing the entire airdam assembly by drilling the rivets holding it in place. The foglight kit actually contains replacement rivets to reinstall it (use a standard simple rivet tool). If you feel a little challenged here, it is POSSIBLE to perform the cuts with the bumper in place. There are oval scribe marks on the inboard side of the trim, and you can use these in combination with a mirror and/or car ramps to make the cuts using a utility knife. It will probably take longer this way; the plastic is tough and thick. I found the biggest challenge was attaching the two screws on the lights into the frame piece. The holes are predrilled - "sort of", but there's very little room to get a tool onto the screw heads. I eventually got it done, but a special "sidewinder" wrench would have helped.

Also, there is no adjustment to the computer on the '95 850.