I tried to find the harness to connect to the MAP sensor today, but ran into difficulties. no one has this harness in stock (pep boys, autozone, advance auto, and GM dealership), and even if they can get it, it is expensive. (pep boys could order conduct-tite PN 85146 for $23, or GM dealer could order 15305891 for $35, or gmpartsdirect.com has it for $25 shipped)
At Advance Auto, I did finally find a book by Calterm with pictures and descriptions of electrical connectors/harnesses, and I found two possiblilities but they claimed that they couldn't order either of them. (wtf?)
In case anyone else is able to find these parts, here is the information:
Calterm PN 08658 replaces GM part number 12085502, and it is for a GM MAP sensor (the picture looked like the correct style). this one should be a direct fit, with the notch in the harness.
there was also Calterm PN 08826 which replaces GM part number 12085507, and it is for a GM A/C pressure switch. (I think that this is the same as the conduct-tite PN 85146 harness. Calterm PN 08826 will probably require modification like the conduct-tite harness).
so that's the best that I've been able to find so far. I saw that others have found the conduct-tite harness for ~$10 at pep boys, but no such luck for me.
Also, it appears that the 3 bar map sensor is available through many auto parts stores if you ask for a MAP (or barometric) sensor for an 89 Transam 3.8L V6 turbo.
edit - see
http://rdmelton.autoeducation.com/ca.../boostlog.html for MAP sensors that will work