P-Leads

[gliderman]

Hi All
gotta make new p-leads....

recomendations please on:

-wire to use

my old p-leads had the capacitor on them- are they required and if so where to get them

thanks all

Shane-o

[tferraro]

18ga shielded wire... ground the shielding at one end (the Mag) The capacitor is to reduce the noise the mags generate in the electrical system and comes across the radio as clicking noise. You should reinstall them or you can look for new ones at Aircraft Spruce. They list them for 79.95 each if you search under noise filters .

[piperrocks2013]

Hi All
gotta make new p-leads....

recomendations please on:

-wire to use

my old p-leads had the capacitor on them- are they required and if so where to get them

thanks all

Shane-o

Shane chances those capacitors are well worn out and dried up by this day and age. I would scrap them. Providing you don't have any serious interference, most newer radios are not as suspedpidle to noise as they use to. Just Makesure to use single shielded wire 18 gage. Assuming they are bendix unsolder the tips and resolder new wire tip heat shrink shielded wire and crimp a new terminal screws that to magneto casing . Do the same with two terminals on the end, makesure use heat shrink so it doesn't accidentally ground itself on the key side of things. Other way is to cut the shielding solder little piece of wire to the shield heat shrink and add terminal on the end. Reinstall. Don't waste money on new plead hex least yours are in terrible shape. You should be good to go!

[Allycat]

My electrical engineer advises to ground both ends of the shield (on magneto P leads only). Provides a secondary if main conductor fails.

[pa20]

IIRC...Leaving the shielding ungrounded at the switch end is done to preclude radio interference.

[deandayton]

IIRC...Leaving the shielding ungrounded at the switch end is done to preclude radio interference.

Connecting the shield at both ends will result in a ground loop. This is a bad thing for radio interference.

I don't understand the comment about providing a secondary path. It wouldn't allow you to "turn off" the mag.

[richas]

Yup, only ground one end.

Rich

[piperrocks2013]

Connecting the shield at both ends will result in a ground loop. This is a bad thing for radio interference.

I don't understand the comment about providing a secondary path. It wouldn't allow you to "turn off" the mag.

Its possible not saying your wrong. most interference problems is not from bad pleads or how it's necessarily wired, but a cracked casing in the coil bad spark plug leads where carbon tracing occurs. I know most of planes been around ground the shield on the mag and the ignation. Reason for this its to damn makesure that mag is grounded! Let's not forget are engine is rubber mounted and has a grounding strap. (Least it should) I have wired professional recording studios from scratch and when it came to high impendance and tube amps!! Let me tell you shielding and grounding became everything or you pickup 60hz hum could even damage our op amps if not rectified . You could just shield the one side probsbly be right way to do it as its done in audio lines like this also, I have also read where they want the shielded grounded both sides. Sometimes on situations like this it's trial and error with little art involved.
I purchased couple p leads from Spruce last year and they wanted it shield connected at the key and magneto. Everything seems fine. My other Pa 22 is wired the same way accept they have two filters just like Shane was talking about. If interference is bad and you have rectified all other causes then only would I say start putting in filters and altering shields on pleads. Onlything I personally suggest reroute your pleads away from audio or dc wiring going to the radios. On both pacers went stright across keeping the wires away.

Jared

[Glen Geller]

I believe the shield is crimped between the two ferrules that gets captured between the Hex nut and the magneto body.
The core wire gets soldered to the washer with a rounded blob, and the phenolic spacers load it against the internal contact of the mag.
The switch end of the shield should have a ring terminal to the ground terminal of the switch.
All six of our club Shortwings are like this I think.

http://s124.photobucket.com/user/Her...a00b8.jpg.html
http://www.aircraftspruce.com/catalo...hex-pleads.php

GG

[Allycat]

IIRC?? Yea what Jared said.