I couldn't find a problem with the tach wiring with the cluster installed. So I pulled it back out tonight. I must have done something wrong when I reassembled the cluster. I should have taken pictures of every nut, washer, lock washer, nylon washer, etc. when I removed it.
Here is a series of pictures that shows how it was installed. Do any of the nuts, washers etc. look out of place?
There's a bunch of pictures. I'd rather show you everything since I have no clue what I did wrong.
Here's a shot of the two nylon washer that I installed between the ribbon and the housing on the 12 volt coil posts:
Some people think a picture is worth a thousand words...