rev counter

In the last few months I notice that when i turn the igniton key to the off position the rev counter reads 8000 revs but if I turn the key one turn and turn to the off position again the rev counter reads zero. Can anyone explain ? I read that it maybe the regulator/rectifer that could cause this. Indeed the regulator did stop working but it was replaced with a new one but the rev counter still reads 8000 revs when i turn the key to the off position. The engine is a Mariner 40hp 2 stroke.

Any ideas ?