So I exchanged that sensor and it still doesn't work. I have 5v at the connector. I noticed that my odometer and trip meter didn't move at all so I checked on the trans and found this. I'd like to fix this wiring mess. Where are they going? Under the dash or the hood?

 

You should be able to find a schematic online somewhere. Pretty sure the VSS runs to the PSOM on the back of the instrument cluster.

 

It's a 2000 diesel with mechanical odometer, if that makes a difference. The connector on the tail of the trans has 2.8v going to it. As crappy as the wiring looks I don't think that's the problem. I do need to replace that connector though. I have a 4x4 trans I might be able to try a sensor from assuming they use the same one.

 

The vehicle speed sensor is on the rear differential, not on the transmission. The speed sensor on the rear of the transmission is the output speed sensor. The 4x4 uses a different sensor, they are not interchangeable.

 

Ok thanks. Is there an input speed sensor on the trans too? I don't suppose there's a way to test these sensors is there Mark?

 

There is an input and output sensor on the transmission. They are both on top of the trans, one near the front and one near the rear.

You can check each sensor for resistance. Somewhere around here is the ohm value that you should get.

Nothing that either the input or output sensor does can make the speedo bounce. The vehicle speed sensor can do that.

 

 

So I did a little test. On my '01 SD350 I pulled the connector off of the sensor on the rear end and drove it. The speedo still worked like normal with no issue. I think it's got to be one of the other sensors or the cluster that's bad.