Tach help
 

I have installed a Pertronix system to replace points, this worked good with no problems, except:
1972 - 107
116.982 engine

After installing tach has gone crazy. At idle it shows 2000 rpm and jumps up very quickly to 7000 when apply gas.
They(Pertronix) recommended this:
2 - inline 3 amp, 400V rectifiers, did this and no tach responce
1 - inline 3 amp, 400V and tach idle correctly but, apply gas and jumps very very quickly to 7000

Tach did work before.
Seeking to replace tack but none seem available.
Please help, do not want to go to a aftermarket.
Thanks,
Tim