MSD with Rallye Tach

[smokinjoe]

Does anyone know how to get my factory rallye tach working with an MSD ignition (6al)? Do I need that adapter kit and does anyone know the part number?

[69ChargerRT]

you definitely need the msd adapter.  i dont know the part number bu it should be on the msd site.  my buddy used it wih his stock tach in a charger and it worked fine.

[GregGarner]

There are actually two ways to get your tach to work. One way is to use the MSD adapter. The other way is to put my new replacement tach board into
your tachometer.  See my website for more information on the replacement tach board kit:

www.rt-eng.com

The reason that the original tach board does not work is because mopar designed the tach board to trigger on 56V. When your original points opened, the electrical
field inside the coil collapsed, and the coil (an inductor) then generates a somewhat higher voltage than it originally was supplied with. I have measured many coils
to put out 250V spikes that last only about 5 microseconds. This spike is what the original mopar tach board would trigger on. The MSD ignition output is a nice clean
square wave that is either at 0V or 12V, so there is no voltages present that can trigger the original tach board.

GregGarner
www.rt-eng.com
Home of the mopar clock and tach repair kit