I'm currently buying a newish instrument cluster for my 99 XJ... Is there any way to roll the approximate mileage from my old dummy light cluster to the new one?

 

Not unless the dealership has some way of doing it.

 

This video should explain to you what you need to know.

 

Theres no point, the mileage is stored in the ecu not the cluster. So just plug it in and it will read correctly.

 

Nope there are stored in both ecu and the cluster so unless you match the mileage to what you had before, you can get a mil light for incorrect mileage not matching. And the dealer is the only one that can flash the mileage in the vehicle to match the cluster. Also it will still count if cluster is pulled off.

 

Any Repair shop that uses the Snap-on Pass-Thru Pro software can reflash the correct Mileage into the IC for you. Chrysler (for a fee) allows independent Repair shops/dealers access to three primary functions (required by Federal Law Now, but not limited to Emission control devices only) Reflash the SKIM modules, Reset Vin Number from used Computers, De-activate SKIM for vehicles not equipped with it from the factory and to Program New Computers after installation, also allows independents to Reflash/Update ECM/PCM to newer software when it becomes available.

So you can take it to the dealer or shop the phone directory for a local shop who has the required equipment to do the reflash.

 

The '99 stores the mileage in the cluster. If you swap them it'll display the donor XJ's mileage. PCM won't care.
Check the end of this thread:
http://www.jeepforum.com/forum/f11/2...-reset-820964/
It says you can swap IC #13 and the mileage will follow. I cannot vouch for accuracy and have never tried it. Thought I'd point it out though.