Using magneto as RPM source?

[jbagley]

My panel was wired before I got the kit. Currently, the tach is wired to the left and right magnetos as an rpm source. There is a switch to select which magneto it is reading from. During run-up if I don't flip the switch when I switch from one mag to the other then I lose rpm indication entirely... Seems odd. Is this normal?

I am replacing my tach with an MGL mini-extreme. Would like to do away with the switch to select which mag to read rpm from.

The MGL documentation just says to wire one magneto directly as the rpm source, but won't that mean I don't get an rpm reading when that mag is turned off?

[Mark Burns]

James,
It's normal to loose the RPM indication if you forget to flip the switch.
You've just grounded the P-lead wire.

And to answer your second question, yes you won't get an rpm reading on the mag without the wire to the rpm source. It's not a real problem at all.

My 7A has just one mag wired to the EIS. I check the other mag first and note the feel of the drop. Then I check the other mag, the rpm on the EIS goes to zero but I "feel" the engine to know all is well (or not).

I thought about the extra switch to get a reading of rpm from both mags but decided to keep it simple and I'd recommend you do the same.

Mark

[aerhed]

The magneto RPM sensor that MGL sells reads tach whether the mag is on or off. Mag check is normal, shows RPM on either mag or both. Works great.

[David-aviator]

Originally Posted by aerhed

The magneto RPM sensor that MGL sells reads tach whether the mag is on or off. Mag check is normal, shows RPM on either mag or both. Works great.

I checked this thing out, it appears it is designed as a rpm input for one of their EFIS systems. Are you using it with EFIS or does it work stand alone?