Using Aux Output on Smiths Voltage-sensing tach

[kurtd]

I had my Sunbeam Tiger tach converted to a voltage-sensing tach from a current-sensing tach (by Nisonger Instruments (http://www.nisonger.com/mechanical-tach ... rsions.htm). Inputs to the tach are 12v power, ground, and tach signal. I set up Aux 2 as the tacho signal and connected it to the signal in of the tach, but no movement of the gauge. Is there something else I need to be doing?

The conversion is typically done to enable the Smiths tach to be used with a pertronix electronic ignition and a conventional distributor, but I have also gotten this to work with the tach output of an MSD 6a ignition box (and a tach adaptor unit also sold by MSD).

Thanks for the help,
Kurt

[AdamW]

The aux outputs only pull to ground so you often need a pullup resistor with many older tach designs. Newer tachs have the pullup built in.
So find yourself a 1Kohm 1/4w resistor and link it accross your tacho input (aux out) wire and a 12V supply. If you can get access to the back of you tacho then it's probably easiest to do it there, otherwise you could alternatively do it at the the ecu end of the wiring.

[PQatPIT]

Aux2 is able to drive output to both 12V and gnd by setting Output Mode to 2(Both). Usually this helps with newer gen tachos so no need for pull-up resistors.

[kurtd]

Thanks for the recommendation. Unfortunately, when I set the function of Aux 2 to Tacho, I don't get an option to set the output mode to 2 under the list of settable parameters for Aux 2. Am I missing something?

[PQatPIT]

Oops, my bad. Seems that pull-up resistor is the way.