Autometer tach with a Vertex magneto

[Sam K]

So I'm going to install a Vertex Mag in my bug and I've got an Autometer monster tach in it. I've done a lot of research on several forums and websites and I've found tat some people have hooked their tach directly to the mad with no trouble and some peole say you need to to run signal converter. I bought an Autometer 9118 signal converter and the instructions say that it's for magnetos with an external coil. Does anyone here have any real world experience with this setup? Thanks!

[2332-64]

Sorry but you cant wire an standard DC Autometer tach to a magneto and expect it to work or even be accurate.

I’m currently running a Don Zig mag with internal coil and a autometer 9118 tach convertor which uses the signal from the p wire.
 
Follow the fitting instruction that came with the 9118 convertor and you will be fine.

A couple of things I will say is that you will need to use shielded cable from the P wire nut to your convertor/mag switch. If you don’t the tach can jump and flick now and again as the solid wire core HT leads broadcast nasty radio frequency.
 
Don’t use standard suppression HT leads or spiro core on the mag as that will neuter the magneto output and remember to reduce your spark plug gap to .018 - .020 and points gap should be .015 -.016.
 
I’ve mounted my 9118 convertor under the rear seat away from the mag and used shielded wires to the convertor from the mag. I’ve also shield the convertor unit and put a inline 20ohm resistor just before the tach.

My Autometer tach works perfectly and I’ve tested it for accuracy and it is spot on.

Hope this helps Jason  

[K-Roc]

Also if you are in the need of a rev limiter, or RPM window switch for a shift light etc...

These guys have great products.

http://www.etcrevlimiters.net/

[Sam K]

Thanks for the advice! I assume the P wire from the mag is the terminal that you attach the magneto kill wire to? i was planning on mounting the signal converter behind my dashboard. Also, what is the purpose of the resistor in the wire?

[Lanny Hussey]

Back when I ran a mag, I wired up a relay between the ignition switch and the P(mag ground). Turning the key off would throw the P to chassis ground, killing the mag. That way the engine would run and shut off without needing an extra switch.

[2332-64]

Thanks for the advice! I assume the P wire from the mag is the terminal that you attach the magneto kill wire to? i was planning on mounting the signal converter behind my dashboard. Also, what is the purpose of the resistor in the wire?

Yes the P wire is the wire that goes to the mag kill switch.

As said above you can use a relay of the ignition instead of a separate switch, it just depends on personal preference.  The resistor is just to smooth the signal to the tach to limit any spiking.