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brianjohnson
05-19-2013, 05:48 PM
Does the EFIS chassis ground wire on the main harness expect the EFIS to be grounded through the panel? I have aluminum panels but they are mounted in a fiberglass shell and there is no connection to aircraft chassis ground. I've been troubleshooting an erratic CDI indicator so I am making sure everything is properly shielded and grounded and I assume the chassis ground wire is attached to the serial port shields?

Rob Hickman
05-19-2013, 09:36 PM
You should have a 14-18 ga ground wire connected to the EFIS case ground screw.

brianjohnson
05-20-2013, 02:35 PM
I guess I should be more clear. I have the factory wiring harness and the short ground wire from it is connected to the case screw. The panel the EFIS is mounted in is not an aircraft ground, is that a problem or not?

Rob Hickman
05-21-2013, 10:10 AM
I guess I should be more clear. I have the factory wiring harness and the short ground wire from it is connected to the case screw. The panel the EFIS is mounted in is not an aircraft ground, is that a problem or not?
Yes, you need ground wire from the EFIS to your aircraft ground.

151

brianjohnson
05-21-2013, 10:56 AM
so in addition to attaching the short black wire from the factory wiring harness I also need a second wire going to aircraft ground? If so, should it be to the common ground point or just the chassis ground like you would use for a shield ground? Thanks.

Rob Hickman
05-21-2013, 06:23 PM
so in addition to attaching the short black wire from the factory wiring harness I also need a second wire going to aircraft ground? If so, should it be to the common ground point or just the chassis ground like you would use for a shield ground? Thanks.

The short black wire is only connected to the shields in the cable. You need to connect an 18ga wire from the ground screw to a good airframe ground.