Speed Transducer Testing Cruise Control Dead

[mcguirjf]

Greetings,
I've done my searching and need help in identifying a cruise control issue. I does nothing! I read the MBCA article for testing the speed transducer and it states to test for resistance across the two pins. There is also a third pin that plugs into this sensor. I can get a resistance value from one of the two pins to the separate third pin, but no resistance between the two pins. Has anyone ever found their speed transducer to be defective? $50 dollars vs. $200 for an amp is pretty significant business case.

I only found one case of speed sensor fault but the guy was missing the speed transducer all together!

Please let me know if I'm testing this thing wrong.
Thanks

From the MBCA article:

Checking the speed transducer:

1. Remove the left hand cover under the instrument panel.

Note: On early models, the transducer resides in line with the speedometer cable. On later models, the transducer is a small black box, about 1 inch square, that is mounted on the back of the speedometer head.

Note: You may have to push the instrument cluster out of the dashboard to reach the backside of the speedometer.

2. Unplug the 2‑pole connector from the transducer.

3. Connect an ohmmeter to the transducer.

4. If on early models you don't see 50 to 106 ohms and on later versions you don't see 650 to 1370 ohms, replace the transducer.

If these steps do not solve your cruise control problem, then the control unit could be at fault.

[mbdoc]

The 1990 300D uses a "hall effect" type of sensor, and that type has different testing protocols.

They have always had issues with that sensor.

[mcguirjf]

Thanks M.B. Doc!

Do you know what the testing procedure would be or where it's located in the FSM?

Thanks again,
James