Saturday, March 7, 2009

No fun with wiring harnesses

This week I started making a wiring harness for the ICOM A210. The power connections seemed simple enough, although the power lead has to come from the Vertical Power system harness. None of this is installed yet and I haven't figured out exactly how to put all of this together on a bench yet. By the way, PS Engineering provides a really nice Powerpoint presentation on making wiring harnesses.

But it's the audio cabling that has me confused. I'm using a PS Engineering PMA 1000 - II intercom. The 210 comes with an intercom function, bu the PS Engineering intercom comes with a digital recorder that automatically grabs the last 60 seconds of communication and I think that could be handy feature ("what altitude did he tell me to descend to?").

Here's the schematic for the ICOM A210 (Click to enlarge). Note the three different wires heading to the audio panel, which I assume in my case would be the PMA 1000 II. It's labeled as auxiliary audio 1 ,3, and 2. But what is it on the PMA?

Here's the schematic for the PS Engineering 1000 II (You'll want to click it to make it full sized). I'm a little confused by a number of things like (a) Where do the "audio low" and "audio high" wires go? (b) If my push-to-talk switch is yoke mounted, how do I square that with the apparent callout for a three-wire shielded cable? One of those wires would have a very long run. So what happens to the shield, let alone the other two wires? (c) There are connections out of the ICOM to the microphone jack. There are connections out of the intercom to the microphone jack. Do they end up at the same spot?

It's also entirely unclear to me where the three wires that are shown in the ICOM schematic as going to the audio panel, go on the PMA, if anywhere.

I think the problem is that I need to see this as one giant schematic, rather than two.

This is the first chance I've had to try to square away wiring disagrams for two different components. I could some advice what what they're telling me to do.

I could throw $200 at someone and just have them make the full wiring harness, but part of the reason for building the airplane is for "recreation and education," and I'd like to learn how to do this.

Still, I think this is a job best left to SteinAir.

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