Alternator caused speedometer to fail...?

Hi - I own a 98 Honda Civic with about 123,000 miles. About 6 weeks ago, I was driving about 50 mph and all of a sudden the speedometer went from 50 mph to 0. I was still able to drive until I came to a full complete stop. There, the car wouldnt start; after several hard cranks, I managed to get it to start and drove to a nearby autoparts store to replace the battery.

No problems until few days ago when car stopped completely again at a red light, managed to get it to start and this time decided to change the alternator.

Now the car is dead at the driveway :uhoh: and decide to get opinions on this forum before I bring it to a auto place so at least I have a clue of what to tell the mechanics.

Could it be the Speedsensor thats causing the car to stall or maybe the alternator I replaced is defective ?? :disappoin

Thanks

Mechanic replaced the ignition switch today; the switch was burned out due to the alarm system. It was the primary reason why the speedometer drop from 50 to 0; thus causing the car to stall. Feel a lot safer now. :)