GRT Avionics

Does the installation of a resister tapping into the P lead of a magneto to the EIS unit interfere with the conducting of a magneto timing check? Typical procedure is to hook up the timing indicator, turn the mags to "ON" (which is really un-grounding the mags) ((and yes, the sparkplugs are on the bench)) and then do the check. If there is a connection in the P lead line through the EIS box does this make a problem?

Thank You.

Tim Hickey

I have the resistors and my buzz box works fine. One reason the resistors are there is so that if the EIS fails and shorts to ground the mags will still work.

Interesting point about the EFIS or the interconnect wiring failing and shorting to ground. Your point out that the resister is there to prevent grounding the mag. I had been planning to tap into both mags so that on a mag check I would maintain the display of the RPM, but maybe the wiser move is to not mess with one of the mags so as to guarantee that a short/failure in the EFIS doesn't take both mags off line. What do you think?

Tim Hickey
Montrose, Iowa.

tjhickey wrote:maybe the wiser move is to not mess with one of the mags so as to guarantee that a short/failure in the EFIS doesn't take both mags off line. What do you think?

The EFIS isn't connected to the mags, so it won't take either of them out if it shorts or goes dead.

The EIS has two separate inputs, one for each mag, and each has the resistor which protects the mags from shorting if the EIS shorts or goes dead.

-Dj