MSA 6A with factory Tac

[dvader]

I have a 69 roadrunner that has a MSD 6A ignition installed that I am trying to get a factory tac to work in. I sent the tac to Performance Car graphics to have it calibrated and have a new circuit board installed. I also sent the 6A box to MSD to fix the tac output which was bad. I hooked up little aftermarket tac to the 6A box in the car and it worked as expected. The factory tac installed back in the dash with the 6A tac output wire connected blade terminal on the tac will go p to ~600 RPM when the car is started and raise when the motor is reved up but but stays at the highest RPM obtained until the ignition is turned off, then it instantly drops down back to 0 RPM. Does anybody have any experience with this combination? Do I have it hooked up right? Should it be hooked to the negative terminal on the coil? Any help would be gratefully appreciated since I have called everybody I can think of and they just send to somebody else. Thx.

 

[440+6]

You need a tach adapter (filter) to make the older ones work, newer aftermarket tachs have it built in I believe.
Ran into this a few years ago with a buddy's car and that fixed it.

 

[dvader]

The new circuit board is supposed toeliminate the need for filter. Thx though.

 

[Car Nut]

You need a tach adapter (filter) to make the older ones work, newer aftermarket tachs have it built in I believe.
Ran into this a few years ago with a buddy's car and that fixed it.

X2

MSD told me there's no other way to fix it without a tach adapter.

Have you called MSD?

 

[kiwigtx]

x3 on the MSD Tach Adapter....That's the only way my factory tach worked when I ran an MSD ignition unit. :icon_thumright: