Mechanic Q: I have a 2003 Merc. Marauder that is having a electical?

I have a 2003 Merc. Marauder that is having a electical issue... Something is cause the ECM fuse located under the hud to blow. Which of course shut off the engine. But it also causes the speed-o-metor to twich. It jumps up to 80 mph then back to zero. And security light in the window flashes like the alarm is sounding... What could this be?