Factory tach with HEI

Mine works fine.

The early AMC products used a tachometer that was "in series" with the points (or as stated the ignition) but did not act as a ballast but as an AMMETER to measure the current flow through the points as the engine ran and calibrated to read RPM rather than AMPS. Tachometers from early up through believer 1974 for the V8 cars were that way and became pulse triggered tachometers after 1974. The I-6 cars remained of that type through end of production.
My 1974 TSM indicates the Javelin was a pulse type tachometer with all others being in series thus the pulse triggered tachometer for Javelins might have changed with the hump fendered models of 71,2,3 and 4
Thus if you are planning on going with HEI look into the adapter that is available to continue the use of the factory installed tachometer IF using a V8 74 except hump fender Javelins or an I6 car with tachometer up through end of production.
That said this comes from memory of messing with this subject some time ago and I think I am correct.
The V8 of course was no longer used from 1980 on in the cars so a V8 Hornet/Concord or Spirit based AMX would be the question mark and probably in series type.

Edited by uncljohn - Nov/23/2016 at 2:03am

WesternRed, how is your tach wired? My understanding is that the factory tach was wired in series in the ignition system, and that it replaced the ballast resistor wire that was used in cars that did not have a tach. (Isn't that why the pink wire at the starter solenoid was left disconnected on factory tach cars?)If I wire the tach into the 12V ignition feed wouldn't the tach's resistance value prevent the full 12V from reaching the distributor? Or am I totally off in left field (again!) Any insight would be greatly appreciated.

Thanks for all of the responses. I'll play with the tach and wiring a bit and see what happens.

Ralph G. wrote: WesternRed, how is your tach wired? My understanding is that the factory tach was wired in series in the ignition system, and that it replaced the ballast resistor wire that was used in cars that did not have a tach. (Isn't that why the pink wire at the starter solenoid was left disconnected on factory tach cars?)If I wire the tach into the 12V ignition feed wouldn't the tach's resistance value prevent the full 12V from reaching the distributor? Or am I totally off in left field (again!) Any insight would be greatly appreciated.

Mine is wired in series, the same as factory and works fine, I did remove 2 separate sections of resistor wire from the circuit.