I agree with KTM.

If u have proven the Rescue 911 ribbon cable and power supply to be "independently" working perfectly, it can only be the DMD itself.
* Prove your 911 ribbon cable and 911 power work correctly by putting the fishtales dmd into your rescue 911 with both of its 911 power n ribbon connected..If the fishtales dmd works perfectly, its your dmd from rescue..

If its not the DMD from rescue, it can only be a faulty 911 ribbon cable or 911 power supply.

Had already tried that Cavey and the fish tales display does not work in Rescue. Ribbon cable is ok cause it works in fish tales.