Here's some information for anyone who wants to repair a defective 996 cluster (for example my 996 cluster had a bad lcd) with the good circuit board from a 986. The benefit for me was that I was able to perform the 996 cluster swap by using a defective cluster that cost me $155. It looks like non-defective 996 clusters cost $500 or more, so the savings are significant. In addition, you can swap over the mileage from your Boxster without sending it a speedometer shop. One shop is charging $200 for this service. Gavin Yuill was the person who figured this all out, so he should receive the credit.
Please note - I did this using a cluster from a 2000 996 and a 2000 986. These are the "old style" clusters with the blue, white and black connectors. I don't know if it will work with the "new style" clusters. Also, if you try this at home, you assume all the risks.
The good news about swapping the circuit boards is that the MY 2000 986 and 996 circuit boards are identical. The bad news is that the programming in them is different. In my case, this meant when I attached my 986 circuit board to my 996 gauges the voltmeter didn't work. I also expect that the analog speedometer would be off by a bit and the mileage would be incorrect.
As Gavin says in his post, the way around this is to copy the programming from the 996 circuit board and write it to the 986 circuit board. At the same time, you can copy 3 lines of code from your 986 and use it to update the mileage and the Vehicle Identification Number from your Boxster. You can probably also turn on the cabriolet top operation light and the on board computer as well. However, I did not have to do this in my car. Perhaps Gavin can share this information too.
In order to do this, you need a device called an Eprom programmer. You also need a clip to attach the programmer to your circuit board. On my model year 2000 circuit boards, the chip is above the center lcd and slightly to the left. Here's a picture of the set up:
Here are the basic steps you will follow:
1. Connect the programmer to the Carrera circuit board.
2. Download the programming from the Carrera cluster and save it to a file. (On the EPROM programmer I bought I was required to "swap bytes" when downloading. There is a selection in the programmer software that does this automatically.)
3. Disconnect from the Carrera circuit board and connect to the Boxster circuit board.
4. Download the programming from the Boxster chip.
5. Copy the first line of the Boxster programming and use it to overwrite the first line of code in the file containing the Carrera coding. (This contains the odometer reading. It's encrypted, probably as a deterrent to odometer fraud.)
6. Copy the second half of the second line of the Boxster code and copy it to the second half of the second line of the Carrera code. Copy the first half of the third line of the Boxster code to the first half of the third line of the Carrera code. This updates the VIN.
7. Save the modified code to a new file.
8. Write the modified Carrera code file to the Boxster chip
9. Reassemble everything and you're done.
Here's a picture of the computer code that I copied from my Carrera chip. Note how the VIN starts in the middle of the second line and ends in the middle of the third line.
Note that the EPROM programmer and the clip to connect to the board cost about $140 shipped. I'm willing to sell mine at a discount to anyone who needs to do this. Just send me a PM if you are interested.