obd 1

[fixkick]

no power, the 91 has DLC next to the battery there is no power there, like in 1996+ cars.
its just a 2 pin jumper seen here, infact the page is a 91 geo.
as you saying the DLC is missing,?? it has black cap on it , if still liike new.
if its missing the harness would be hacked all to hell here.
see the red body here, its a 1991 geo tracker, verbatim.

http://www.fixkick.com/CEL/DLC/DiagJump.html