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Electrical questions...

kbalch

Well Known Member
I've been mounting the many little Garmin boxes on my sub-panel and am beginning to run the various wires forward through the firewall. A few questions:

  • Page 43-12 Figure 2 shows the WH-P909 running back from the alternator through the firewall. Where does it connect?
  • I received a shunt from Stein with my Garmin sensor kit and have ordered a 60amp ANL fuse and mount. My understanding is that the P909 will actually run to the fuse and then I'll make up another short wire to run from the fuse to the shunt and an additional short wire to run from the shunt to the starter relay. Is that correct? If it is, can the shunt-to-relay wire share the P912's post (43-04 Figure 1)?
  • P912 is shown on 43-01 penetrating the firewall, but where does it connect? I'm assuming that it should be hooked to the empty terminal on Stein's main bus strip. That's a 4-post buss bar with two posts used by the avionics relay and one by a wire labeled "main bus."
  • The GEA24 EGT & CHT sensor wires are quite long - can I simply cut them to the needed length or must they remain full-length? I seem to remember from my last project that those wires shouldn't be shortened, but it's been a long time and I could be completely wrong.
Also, any opinions (always a dangerous question!) on hiding the GPS antennae on a bracket under the cowling? I did this on my -8 years ago, but it was a VFR-only airplane, while the -14A will be an IFR machine. I?d like to hide the ugly little pucks if I can.

On the -8, I built a bent aluminum bracket which I riveted to the firewall. I just happened across this alternative idea the other day:

http://www.vansairforce.com/community/showpost.php?p=874725&postcount=4
 
Also, any opinions (always a dangerous question!) on hiding the GPS antennae on a bracket under the cowling?

They seem to work great under fiberglass .. not so much under aluminum :)
 
IMHO it is technically illegal to install a TSO?d gps, intended for ifr use, unless you follow the installation instructions in the TSO installation manual. That says to mount the antenna externally. Now, 99% of the time it won?t matter, just like 99% of the time a 3rd EFIS is just dead weight. But equipping for IFR means thinking about that 1% chance.
 
To add a bit to what Bob said, there is a minimum length of coax that is required for a Garmin IFR GPS, so don't go the shortest path/length. I have also heard of issues and shorter life of a GPS antenna on the hot side of the firewall.
 
Assuming that you will have more then one IFR antennae I see no problem with mounting them under the cowling. Mine have worked great for many years. Proper cable length has been mentioned, the othe limiting item is NO metallic paint on the cowling.
 
Both P909 and P912 connect to Stein's main bus. P909 goes through the ANL fuse and shunt prior to the main bus. You can do it the way you described, but P912 is already in the cockpit.
 
Thanks, all, for the input. I'm still undecided on the antenna location, but will bear all of the comments in mind.

Regarding the shunt installation, I believe that I have that in hand now. Thanks, Turner, for spending a bit of time on the phone with me last night and for sharing a few photos of your installation. Much appreciated!
 
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