Just got the car, so very unsure of history relating to this specific issue. 
CEL is on most of the time. Speedometer and odometer are not working. 

I pulled the cable end from the passenger side of the transmission and checked out the slotted end—appears to be intact. Tried the drill test to see if that triggered it—nothing happened. 

My research suggests it’s an ECU communication issue, just wondering if I need to pull the instrument cluster and investigate that end?

Reach up there following the cable from the firewall slide your hand until you hit the backside of the cluster. Press in and then check. 

Dashboards and clusters can be removed but you might be able to avoid that. 

Sweet! I’ll see if that solves the problem. Thank you!

Sounds like what moosens said - disconnected speedo cable. 

This will throw a code for the vehicle speed sensor as that is in the instrument cluster, driven by the speedo cable. 

No need to pull the cluster or the ECU. 

Cheers 

Bennie

Had a live lizard escape while my son was inspecting it when old dad told him not to do that. LOL

So has to pull the dash on our 92 Legacy. It was easy enough , caught the lizard , and then learned about how the speedo cable can not quite fit back until all in place and then needed that extra push.

 

 

I did end up taking the dash apart just as an educational journey. I fully disconnected the cable from the instrument panel and then made sure both the reed switch on the transmission and the instrument end we’re fully immersed in their homes.
 

And  I had help doing the drill test again to confirm the cable was actually working. Turns out it only activated when spinning counterclockwise. 
 

Problem seems to be solved!

The only thing is the CEL is still on and I’m wondering if there’s a separate VSS issue. It gave me a code 33 initially, and I haven’t replaced or messed with the sensors on the driver’s side of the transmission at all, and am wondering how those act to influence the operation of the drivetrain. I had done some research that illuminated it a bit, but not sure if I should bother going down that rabbit hole if the main gauge issue is now solved. 
 

I find it hard to believe the mechanical cable has anything to do with the ECU because there is no electricity involved in that particular piece of equipment. 

Have you cleared the codes?