Mk3 Jetta Speedo Broken

Hello. The speedometer on my Jetta suddenly stopped working. Was scooting along at a decent speed when it happened: it just started jumping around until it finally stopped at zero.
Both the speedometer and the odometer do not work.
This led me to think the sender went out. Replaced it with a new part, which did not fix the issue.
What do you guys think?
I know that the Mk3 chassis is well known for having some quirky electrical issues. Is there some way to test the wires that plug into the sender, or should I just assume the cluster is bad and replace it? Car has 140k on it.
Thanks

Mk3 clusters are terrible about having bad solder where the two connectors on the back of the cluster connect to the circuit board inside. Pull the cluster and resolder both plugs. Should fix your problem. It'll give you a chance to replace any burned out light bulbs, too.

It's been a while, but my Mk3 did this as well - in my case, smacking the dash would get the speedo working again - sometimes only for a short time.

I took the cluster out and disassembled - mine had poor soldering at the connector pins for the cable at the back of the speedo.

I resweated the solder at the pins and it was fine until I totaled the car a few months later...

Update: I soldered the rear pins on my cluster. Still no speedometer.
I even plugged in a spare 2.0 cluster I had lying around. That didn't help either, leading me to believe it may be a wiring issue.
Stumped. Should I test the wiring, or is there something I'm missing?

Could be a bad sender and or wiring. The cluster pins are the most common cause in these cars.

Next way forward (for me) would be to locate a schematic and determine where the pins from the speed sensor go (cluster or ECU). Pull that connector and see if you get a small AC voltage on those pins when the diff turns. Alternatively, ohm out the harness and the sensor from the ecu/cluster connector and see if you have the correct resistance to check the sender and the harness in one shot.

Was the spare known to be good? In my case, the board was bad. A replacement cluster, also had a bad board.

-Todd

Mine had a corroded wire at the sender plug a while back.

I’ve found chafed wiring just above the tranny, providing your VSS in the transmission is still good. It’s just plastic gears that I’ve seen melt due to low oil.