Hobbs Meter in a BL65

[charliestith]

I would like to install a battery driven Tach/Timer, mostly just for the engine run time timer. Installation is pretty simple, just some double sided tape or Velcro and a wire wrapped around one of the spark plug wires. This is ok in an experimental but with a certificated aircraft with no electric a non TSO'd instrument and amateur installation, not so much. So, just wondering if I am going to get hit if I ever get a ramp check or if there is some exception for this kind of thing. I know I can use the Tach time, just like to have a Hobbs type meter for total time for maint and flight time logging.

Thanks in advance.