I would Invest in a Haynes Manual.
You can get a distributor's wiring diagram for a 1995 Galant online at places like The Galant Center. You can also find the diagram at Mitsubishi Motors.
Try PAINLESSWIRING.COM
This website has a lot of wiring for many cars including '92 Eclipse. http://www.modifiedlife.com/1992-mitsubishi-eclipse-car-audio-wiring-diagram/
for a stereo? go to the12volt.com
go to __the12volt.com __aojedam
http://www.installdr.com/Harnesses/Mitsubishi-Wiring.pdf
http://www.the12volt.com/installbay/stereodetail/1541.html
Chilton's repair manual (about $20.00) has all the wiring diagrams for your entire car.
You can find a wiring diagram for your 1988 Mitsubishi Gallant at most Mitsubishi dealerships. Mitsubishi service manuals will have the wiring diagram and can be found at most local libraries.
haynes or palmers service manuals at autozone,advance auto, or Orielly's
You can buy a Haynes manual at Autozone. There is wiring diagrams and other trouble shooting things in the book.
go to installdr.com to see how to remove and install a stereo out of any car