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.