EE FAIL on cluster in test mode...bad cluster?

Saw over on mustangworld and one other site that if while in test mdoe on your gauge cluster, if you goto EE and it alternates between EE and FAIL you have a bad instrument cluster. WTF? Mine def does this. However I am assuming my cluster works fine. Minus that v6 gauge overlay someone installed. What gives? How would the cluster be bad? Even went into the speed readout on the display and it was dead on with my GPS. What is normally bad when this happens? I am thinking about buying an entire used gauge cluster on ebay so I get the right gauge face but I can't swap over the display portion with the Mileage read out can I ?
 
yes, you can swap over the whole gauge cluster...I have a Mach 1 cluster in my GT...

I know I had to swap a couple parts around to make it work, but I don't remember what parts needed to be swapped thought, sorry...I do remember it was pretty obvious what parts where what