I am at my wits end with a months long speedometer issue in a 1992 240 wagon. The car is ABS equipped and therefore has the 39200 speedometer that is unique to the 91-92-93 model years.

Several months ago the speedometer just stopped working. The entire gauge just went dead. I searched on the forums and found some suggested fixes. The sender unit appears to be working fine. There were some cracks and exposed wire in the wiring from the sender, so I replaced the harness from the sender to the junction box in the rear quarter panel. I found a replacement unit on a Pick-n-Pull trip and replace the gauge - but the replacement was equally dead. On a lark I sourced a third gauge - and it also was dead. I gave up and installed a speedometer app on my iPhone and called it good for a couple of months, but the dead gauge continues to offend my sensibilities so I'm back at it.

Just today I found an on-line tutorial n bench testing the speedometer out of the car. Its published on cleanflametrap.com in the odometer repair section. It is highly detailed but not specific to the 39200 speedometer in the ABS cars. I ran all three units through the bench test - and all three remain dead. But - the tutorial did specifically state that there "is some confusion regarding the wiring in ABS cars" so I can't say definitively if the gauges are bad or I was running a test with incorrect connections.

Here are my questions:

1. I find it hard to believe that I could have three bad gauges so I'm figuring I am the weakest link in the equation and am missing something (hopefully obvious and easy). Any ideas on my next best step?

2. Is there an on-line tutorial for bench testing the 39200 speedometer anywhere? Or could someone who knows walk me through the process with the correct connections for 12V+/- and VSS+/-?

Thanks in advance for any assistance here - your expertise is much appreciated!