Speedo/Odometer not working, shifts fine and VSS appears to be ok

[trefmawr]

1998 GMC Sierra 2500 5.7 Vortec 4x4 4L80E

Speedo and Odo are not working, but it shifts through all gears no problem. When I have my el cheapo OBDII reader hooked up it has a VSS datastream reading that seams to function fine (reads a correct speed).

I thought it was maybe the air core motor for the speedo, but would that effect the Odo as well? To me it seems like a signal issue. I found the dark green wire coming from pin #4 on the computer under the hood, but I don't have a wiring setup to run a multimeter to it while also driving around.

Is there a wire I can probe under the dash or close by?

Any other thoughts?

Cheers!

 

[AK49BWL]

Transmission gear position indicator work? If not, check fuse #20 in the dash fuse panel.. Do the other four gauges and idiot lights work?

 

[trefmawr]

All the other gauges and lights work, but only the light for '2' on the gear indicator works.

I'll double check fuse #20 though, thanks!

 

[trefmawr]

Fuse #20 was working. I noticed that the gear indicator light for '2' actually stays on for for 3 and 2.

 

[BriGButler]

It took me 3 instrument clusters to fix the speedometer issue I was having (pegged at max when going 40kph).

After switching the air-core motor 3 times and switching clusters back and forth a couple of times, I was able to troubleshoot it down to the circuit board.

Now my Tac and ODO are correct, but my speedometer reads 50kph when I'm going 40Kph, and 100Kph when I'm doing 80Kph.

Could be better but, I'm not too arsed about it.