I applied power today for the first time; no smoke!  Most stuff worked; that which didn't are relatively simple items.  One is the transponder.

It works just fine - as much as I can tell without it being interrogated. However, power application has been messed up. Part of this was because I had to make a judgement call on which power connection did what.

I've enclosed a very lousy, unreadable image of the wiring page from the instruction manual. This is more to jog your memory if you *have* done this.

At the top of the page is pin 15, which is run thru a 3A breaker to "aircraft 12V power".

Mid page is pin 1 - aircraft master on. Note 5 says that if pin 1 is connected to 12v power that this will provide automatic on in the last mode used on the transponder.

I connected pin 15 to an always hot breaker - I figured if power was applied to keep things active with the display off, it should be protected somehow.

Pin 1 was connected to a plain toggle that connects 12V to pin 1. No protection since I figured the main juice would go through the breaker when on.

As a result the toggle that provides 12V power to the xpnder does nothing. On or off, the transponder powers up when the "on" button is pressed.

I'm thinking I need to swap these pins; what has been your experience?

Thanks for any applicable experience you share.

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I have this same transponder, and fortunately, it was installed when I bought the plane. I'm no expert, but I'll try to help.

I looked at the installation manual, and note 5 says "Avionics Master On (pin 1) when tied to 11-33 VDC input (pin 15) provides automatic power up. When power is applied the unit will power up in the last mode selected."

I read this as running power from the Avionics Master On to both pins. I may be wrong, and I don't want the smoke to escape from your unit. As you know, smoke makes electronics work, because they quit working when the smoke escapes.

I've got a binder with all my wiring diagrams. I'll look in it tomorrow afternoon, and get back with you.

I've got a different electronic problem....a stuck mic.  I believe it's in the PTT switch, or joystick wiring, but the only troubleshooting I've been able to do was to unplug the headsets. Also, since it rained for 2 days, I thought moisture had gotten into the switch. I ran a heat gun on it, but no joy.  Next step, look at the wiring diagrams, and see where the wires go.


Darrell, what kind of PTT switch do you have? I'm asking only because I have the Ray Allen 5-button stick grip, and there's a lot of wires (8 in my case) crammed up in the top cap of that grip that I could see one breaking its solder joint and creating the false closed condition.

Carl, I had the same xpdr on my previous build and the avionics shop (Stark Avionics) I bought from provided a wiring harness so I did not have to wire it.  However I dd not like the fact that the Xpdr came on every time the master switch was turned on, so I queried Stark and they told me to cut the wire to pin #1 and cover each end with some heat shrink.  I also did not have an avionics master and turned each item on/off individually.  After cutting the wire to pin 1, that's what I was able to do.

Thanks, Don; I was originally just going to go with power to pin 15, but I was wanting it to power up in VFR each time; didn't play with it beforehand, but now seeing how it works first hand.  I'm using Tyco toggle switch circuit breakers, for each system, so wanted it to be able to powerup when I flipped the breaker, yet "remember" where it was when I shut it down. Easier to flip a switch than look for, then press, a relatively small "on" button on the xpnder face.

I've been studying my wiring diagrams today, and in the 25 pin connecter chart, mine says that Pin 1 and Pin 15 are both wired to Position 1 on the Avionics bus, which has its own master switch. The schematic shows a 3 amp breaker from the Avionics bus.  Hope this helps.

I still haven't found what's causing my stuck mic. I took the control stick and center console apart to get to the wiring. I disconnected the PTT, and it checked ok.  The problem is still showing. The grip is a Tosten CS-8, so yes, lots of wires.  Tomorrow, I'm going to check the headset jacks.  I told my A&P that all this is helping me to learn this airplane. He's going to sign my condition inspection Monday or Tuesday.

Well, I guess mine operates as a "feature."  I did some more searching. Most definitive answers were on the VAF forums. For what I *want*, pins 1 and 15 are both connected to the xpnder power lead.  I did that. I *still* have to turn on the breaker, THEN press on/stby/alt to get the xpnder to power up.

One or two guys mentioned that theirs was wired correctly, but that earlier 327s didn't have the automatic on capability.  Sounds logical. I don't like it, but I can accept it.


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