Tach reading question

This may be a silly question. I bought an RV7 with a Superior 360 that has light speed EI and a slick 4371. Each is connected to a switch. When I shut off the mag, the tach still shows rpm on the EFIS. When I turn off the lightspeed, the mag goes to 0 until I turn the lightspeed back on. Is this normal or should it be setup another way?

Thanks for any thoughts!

It sounds like the tach signal that is feeding your EFIS is coming from the Light Speed and when you turn it off, not signal is provided.

There are a couple of way around this.

One is to install a tach signal generator and wire that to your EFIS and leave the Light Speed out of it.

I connected the mag directly to my Dynon Skyview, which works well. Both the Lightspeed and mag need to be connected to the EFIS.