stopped working and would like to know if it is electrical ( fuse ) or mechanical.

Electrical, mechanical rev counters where obsolete years ago. l have a 1960 is Tr4 and that is mechanical, but anything after 1970s will be electrical

May well just be a dry joint. Nothing a bit of soldering iron work wo not put right.

Theres an earth strap that goes between the gearbox housing and the bodywork which has a nasty habit if snapping, plays havock with the electrics, it is worth checking. Its an electronic rev counter.

Hope this helps