Brakerless ignition system means, that there are no physical
switch in there. But there is an electronic device such as
Transistor or Thyristor wich interrups the circurity of the
ignition coil. All common tachs should work as usual attached
to the terminal at the coil used for the braker circuit.

The line used for the tach should switch between +12V and
ground, you may measure this with an analog voltmeter at
idle. If there is a too weak signal for the tach, I guess there
is something wrong with the coil or interruption circuit.

Helmut
'80 Camper