RPM not displaying

[BSteeves]

I have a lightspeed Plasma III and one mag on a Lycoming IO540. The engine harness is installed with the rpm wires going directly to the mag as instructions show.

The RPM reads fine when both the mag and lightspeed ignitions are on. However, when you shut off the Lightspeed ignition, the RPM display goes to zero. When you turn back on, it comes back as normal.

Checked wire harness for mag and is hooked up per directions.

Any ideas????

Thanks
Brian

[Rob Hickman]

This does not make sense, are you sure you have it wired with the RED RPM sensor? Make sure you don't have the Plasma III wired to the EFIS.