Hey, my interior got ruined since one of the windows decided to cease functioning, stay in the down position, and coincidentally, have a rain-storm all at the same time. Good news is that I had planned on turning it into a track car and pretty much keeping with the rhythm, tearing everything our regardless. One of the things that caught my eye was the instrument gauges. A couple of the bulbs have burned out. Probably not due to rain but anyway. I've torn it out and being a stupid engineer that I am have dissected it to see what was on the inside. Behind, the speedometer (where the odometer sits) lies THREE sets of numbers! Why the third one?

The 6 digit cluster for total miles
The 4 digit trip odometer
The 5 digit I don't know what it is

The main reads 139420
The 5 digit reads 39419

 

They're both connected to what seems like one of the sprockets that moves both

 

That would be the 20,000 mile switch. What it does, I don't really know. But it is an input to the ECU, so I would assume it would switch maps or something similar.

 

Look in the FSM fuel and emissions section and look up Port Air Solenoid and that explains it.