No 4th gear?

[Pace 1989]

Noticed when I was tuning that the ECM never sees 4th gear.
I know the car goes into 4th gear, but it never shows up on Turbolink.
I did a tranny service b/c someone told me the filter could be touching the 4th gear switch and grounding it out.
The filter was fine, and I still don't register 4th gear.
What would do this?
If it's a bad 4th gear switch how do I replace it?
Ken

 

[MeanBuicks]

The 200-4R switches are normally closed, electrically. If your ECM does not see a 4th gear signal, either the switch is bad or there is a short in that wire providing an alternate path to ground.

Since you already ruled out a short circuit, the switch is most likely the culprit.