secondary tach

I posted a question a week or so ago about multi-probe engine monitors.
I decided to go with Electronics-international UGB-16. I can monitor
a total of 16 points. So with 6 EGT's and 6 CHT's, I have 4 spares. I
opted for an OAT function because I don't like the placement of my
thermometer. It's in the vent window where it looks ridiculous and
it's hard to read. I also picked a secondary tach function.
Secondary meaning it can't be my primary tach. The secondary tach gets
it's signal from the p-leads on the back of the mag switch. I didn't
know that the p-leads had any indication of rpm but apparently they do.
Even EI's primary is connected to the p-leads on the back of the mag
switch. I never knew that the p-leads had any pulse or signal related
to RPM. Why is that?
Thanks
Dave
M35

Maybe you can answer your own question...
what does the magneto/p-lead do? What relationship do spark plug
firings have with rpm?



dave wrote:
I posted a question a week or so ago about multi-probe engine monitors.
I decided to go with Electronics-international UGB-16. I can monitor a
total of 16 points. So with 6 EGT's and 6 CHT's, I have 4 spares. I
opted for an OAT function because I don't like the placement of my
thermometer. It's in the vent window where it looks ridiculous and
it's hard to read. I also picked a secondary tach function. Secondary
meaning it can't be my primary tach. The secondary tach gets it's
signal from the p-leads on the back of the mag switch. I didn't know
that the p-leads had any indication of rpm but apparently they do.
Even EI's primary is connected to the p-leads on the back of the mag
switch. I never knew that the p-leads had any pulse or signal related
to RPM. Why is that?
Thanks
Dave
M35