help with rallye tach - wiring diagram?

[The4ork]

i need to figure out how to wire it up correctly to work (none of my gauges work except the ammeter) and have it run off of an MSD Streetfire box

[Chryco Psycho]

there are 2 wires at the factory tach , blue 12 v power & a grey signal wire , the grey wire needs to connect to the MSD but you may need a tach adapter to eliminate the multi spark signal under 3000 rpm so ti will read properly .

[The4ork]

and im guessing it grounds out through the housing?

[Chryco Psycho]

yes , there is no external ground wire

[The4ork]

so should i try running the grey input wire to the tach output off the msd box to see if it works without the filter?

[Chryco Psycho]

you can try it , it will not blow up the instrument, it  just wont read correctly