See if you can find these wires by color
89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
I suspect someone has connected these wires up or just cut them off in an attempt to make the car run.
Is it originally a V8 car?
Hunt around the web and find some wiring diagrams for the 90 model year, veryuseful.com is a good place to start, I like printed stuff but I'm a little old. You will need to trace that harness to put the port wires back together.
I do not suggest using these anymore after I had multiple failures and was forced to open my wiring harness and replace every one of them. The solder joint would brake and give an intermittent connection, I simple use a cold weld connector and heat shrink all connections now.
There is a repair kit consisting of the plastic connector shell and the necessary short pigtail leads with the terminals crimped on. It is available at Advance Auto Parts or AutoZone or maybe O'Riley's Auto parts. The most difficult thing will be getting the parts person steered in the right place to look it up... Electrical pigtails seems to ring a bell for me...