You are going to have to figure out and wire in firewall forward. Using the 85 and 95 wiring harnesses each wire to where they go. Computers are diffenent too so may have to go with complete 95 harness. Man is a GEO worth the effort??
Do as SNKBYT suggested, get schematics for both cars..
Next sit down and do a line drawing of the compilation of both schematics..Get a set of wire numbers (Ace Hardware Electrical Department) and assign numbers to your wires..If you have a wire you need to add, Put an asterisk next to it..so you know it needs to be run..
when done, go to the car, and wire as per your line drawing..adding the wires with the asterisk's (*)..as you go..
When your done and have an operating system, you can get schematic drawing software, (some free on the INTERNET , or at Fry's stores) and make a schematic for your car..will be very handy for the future..