Your '95 GTX has a 278000423 MPEM that comes as a non-dess, but IS dess capeable. It has 7 programable slots in its ROM.
Non-dess has a two wire post
Dess is a three wire post. (Digital Electronic Security System). It was just another don't need item, like guages, to make better sales.
You can open the grey box and jumper the two large solenoid lugs. If that turns the starter, then replace the SOLENOID. Otherwise, remove the starter and disasemble & clean it, it may only need that and new brushes.
The grey box slides into a floor SHOE located underneight it and has a release lever next to magnito side. Gently pull it up to sit on magnito to get the watertite encloser opened. You may need to snip a zip tie or two. Slide the box front back into the shoe and press down to snap and re-secure it. Dielectrical grease all your connections in there and include the fuses and fuse holders. Check all connectors and the black wire negative polarity grounding lug too.
Also look at the HOW-TO section in this forum, or use the search box to find similiar threads on this subject.
Bills86e