TCU tach problems

[WARHORSE]

I have had my TCU for a while and everything tuned satisfactory until lately. I have a 4l80e, I recently connected to my laptop and found either no tach reading or very erractic readings.
Tried to trace my tach reference wire but unable to locate. All other sensors or gauges seem to be working properly. I have the red TCU.
Can someone tell me what to look for and or other possible solutions?

[critter]

First, I think you have to locate and verify the tach wire to the TCU. I'd be looking for places where it's rubbed through and might be grounding out.