Well, I finally got tired of the speedometer reading 9% off the proper calibration.

The cause is the larger tires and the change in diff from 3.07 to 2.88 on the SD.

So, I purchased one of these from Dakota Digital:

http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/category_id=287/home_id=59/mode=prod/prd126.htm


It has complete flexibility for installation and correction of either a high or a low input.

On the W126, the speedometer wire is the white wire on socket #5 of the six pin connector that plugs into the back of the cluster.

Interrupt the white wire. Put the unit in series with the white wire. Connect up power and ground and it's ready to roll.

For the M/B you use "Application #1" with switch #1 off, switch #2 off, and switch #3 on.

Switch #4 is your decision as to whether you want a faster output (switch on) or a slower output (switch off).

If you know your error, you can calibrate the unit while sitting in the driveway.

Mounting it on the W126 is a bit of a problem. I used one mounting hole and secured the unit to one of the three 8mm grounding screws behind the cluster. It sits flat below the cluster and the control switches are within easy reach.

I set the unit to read 9% more speed and it appears to function properly.