Detect the Rpm on vehicles without OBD

[Kind_of_Magic]

Hello all, for an amateur draft I need to detect the engine rpm, but on commercial vehicles Diesel very old who do not have the OBD, type iveco, ducato, etc.. I thought I would connect to the alternator, but before you jump to the oxen I wanted to hear the advice of someone who understands much more? me.

Thanks in advance

[biondo83]

[Kind_of_Magic]

Unfortunately, there is no hand Rpm on the dashboard :(