It's possible the new coil has a different impedance than the
original.  The tachometer requires ~100 volts to work.  It gets this
high voltage from the coil as the magnetic field collapses, the "peak
primary voltage."

For my EJ25 conversion I made a small circuit that recreated this high
voltage from the 5V tach signal out of the Subaru ECU.

Another possibility is that you have bad electrolytic caps in the
tachometer causing it to work marginally.

Ryan

On Thu, Jan 9, 2014 at 1:08 PM, JRodgers <jrodgers113@gmail.com> wrote:
> What's up with this??
>
> I replaced the coil on Volksiebus with a brand new Bosch coil - VW
> spec'd.  The tach worked right up to the point of change, when I
> disconnected the wires, installed the new coil, and reconnected the wires.
>
> Engine starts and runs fine - but for the tach - NO JOY!
>
> Anyone got any  ideas. Everything appears as it should be. It's all
> wired back up exactly like the original coil - wires same places. But no
> tach.
>
> I haven't done this yet - but I can do a voltage test from the +15 pin
> to ground without blowing something up, can I not. Been a long time
> since I've had a meter out for anything but a continuity check.
>
> Suggestions appreciated.
>
> Thanks,
>
> John