I found a scan tool for the Subaru OBD1.  It is free software that you download to a laptop and ties into the Subaru factory plug.  It is easy to make the cable, I just purchased a printer cable, cut the one end off and soldered on a plug from an aftermarket stereo harness that is a perfect fit to the Subaru factory harness.  I purchased the plug and printer cable from Best Buy, See picture.

For more information see:
http://www.graphics.cornell.edu/~v/b10scan/

also see

http://www.vwrx.com/index.php?pg=selectmonitor

The B10 is what I am trying first because it is a simple wire connection.  The Subaru Select Monitor Scan Tool requires a signal translator but has a cool analog display.

Ross, what is a signal translator? Will this work on all OBD1 Subaru's? And how can we reflash our computers after we find out what we have?
Don't let this thread die

I agree - don't let this thread die.  I have been trying to stick to OBDII engines because I have a scan tool to track down problems.  But at the same time, this tool seems like it would do so much more than just provide a code. 

The reflash concept would be a huge benefit as well - with bigger injectors or a turbo on an older motor, it would be great to be able to use the original computer and not have to go to an aftermarket ECU to make it run right.

I have also always wanted a computer screen as a dash - this would be perfect.

Paul...