The International Cessna^® 170 Association

Hi all-

In my quest to not leave well enough alone, I have figured out my winter improvement project for 56D.

Last winter, I made a new shock panel and installed new light sockets and bulbs to restore to factory original using the original style posts and bulbs. While underneath, I noticed some questionable wiring, and while rewiring the entire airplane isn't in the cards at present, tackling smaller projects is.

In 1984, the owner of the airplane installed a Schroers rotating beacon on the top of the rudder of the airplane. While I hate the beacon there, removing it now is not an option. What is curious is that when the beacon was installed, instead of simply installing a switch in the vacant piano key, the mechanic used the radio master switch instead.

Maybe it's the originality nut kicking in after flying Jim Beyer's 52 with Charlie earlier this spring, or maybe it's the fact that I enjoy the utility of an avionics master switch, but I want to restore the use of that key to the avionics master and move the beacon over to the other side of the panel with the other light controls.

I'm not concerned with the the wiring for the beacon or the addition of the switch, but I am a little gray on how to wire the radio master. The airplane has a KLX-135A, an AT-150 transponder, AR-850 encoder, and PS Engineering intercom. Currently, the radios are wired into the main power buss, so their individual switches turn them off. The intercom always stays on, and I presume the encoder receives power when the transponder is on. How much of the IPC wiring diagram is applicable with solid-state radios versus the old tube type radios?

Assume that I am an Etch-A-Sketch and that I have the skills to do quality work, but not the knowledge. I want to treat this as a learning experience and all of the work will be supervised by my IA. Any information and advice regarding a bill of materials and general layout is greatly appreciated.

I appreciate everyone's replies in advance.

I put 81D's beacon on it's own pull out breaker without a switch at all. The pullout lets me turn it off it needed but if the master is on, the beacon is on. It's a good double check when walking away from the airplane against forgetting to turn off the master.

The avionics master would be a switch that would load another bus. The Bus could simply be wires daisy chained from switch to breaker to breaker to breaker but I think a piece of copper is cleaner.

IE the switch would split to three breakers which would then go to your radio, transponder, intercom...
I woudlnt worry about an avionics master breaker as the cumulative of the down stream breakers would (needs to be) less than the capacity of the switch itself.

There aren't many wires in a 170. In fact, you'll probably replace near half of them with the radio anyway.
You might want to consider replacing them all over the winter. Not a hard project and gives you the chance to break out your taxi and landing light to different switch positions (UP Taxi, Down Both, Center OFF)

Each radio needs its own circuit protection, whether fuse or breaker. Like Dave said, these circuit protection devices will receive their power through your avionics master. Find installation manuals for all of your avionics, including transponder and encoder. My Narco 150TSO transponder does not supply power to my Narco AR-850 encoder. Each is on its own breaker. Also, some multifunction boxes (An audio panel with a marker beacon receiver might be one example) MAY have multiple power inputs that you might want to power separately for failure isolation.