P-leads

[bobbynick@msn.com]

I removed my P-Lead connection at the firewall to install new SS firewall, now i am reinstalling it. I have the original insulator parts in good shape, but previously there were just machine screws installed to connect the P-Leads to. what should be there? and where can i get the correct parts?

Thanks

Bob

[Steve Pierce]

I remember machine screws. Have you looked at the parts manual or drawing CD?

[bobbynick@msn.com]

tried to find in the parts manual, but can't find my CD.

[Vagabondblues]

What model of short wing?

I found some use a cover PN/14327, plate P/N 14310 and 4ea insulator washers P/N -81342-74. The rest of the parts are just like you described, machine screws and regular nuts. The only parts that univair has is the insulators P/N -81342-74.

Why not just pass the Pleads through the firewall with just a grommet? A little sealant around the opening where the wire passes through, no break in the line or the shield. You could solder a small braid to the shielding and pigtail it and attach it to the firewall if you were worried about a ground plane fault.

[bobbynick@msn.com]

Sounds good to me, but I am trying to replace according to what ever tech data exist. The only advantage i can see to the original design would be if you ever need to replace the wires as they do get beatup with fumes, heat and oil contamination.

Thanks very much for the direction, this has been a tremendous help. I have the cover, insulator plate and will need the screws/insulator washers.

[andya]

What model of short wing?

I found some use a cover PN/14327, plate P/N 14310 and 4ea insulator washers P/N -81342-74. The rest of the parts are just like you described, machine screws and regular nuts. The only parts that univair has is the insulators P/N -81342-74.

Why not just pass the Pleads through the firewall with just a grommet? A little sealant around the opening where the wire passes through, no break in the line or the shield. You could solder a small braid to the shielding and pigtail it and attach it to the firewall if you were worried about a ground plane fault.

I fabricated a new P-lead harness that way on a twin many years ago and it worked fine.

[Gilbert Pierce]

What model of short wing?

I found some use a cover PN/14327, plate P/N 14310 and 4ea insulator washers P/N -81342-74. The rest of the parts are just like you described, machine screws and regular nuts. The only parts that univair has is the insulators P/N -81342-74.

Why not just pass the Pleads through the firewall with just a grommet? A little sealant around the opening where the wire passes through, no break in the line or the shield. You could solder a small braid to the shielding and pigtail it and attach it to the firewall if you were worried about a ground plane fault.

That’s what I did when one P lead shorted out in the box and while troubleshooting it the second shorted out. Just replaced both as Vagabondblues suggested

[Subsonic]

4 year old thread. Need new info.

I put a SureFly SIM4P in place of my left side Bendix mag with impulse coupler. Right side mag remains. Upon functional check, the Electronics International R1 Tach no longer displayed RPM when only Left mag selected. Worked on Both, and Right.

Called EI and they said to install their "Lumpy Wire" part in place of their previously installed isolator(s) on Left stud of mag switch. Lumpy wire has a resistor and capacitor in it under shrink wrap. Did so, still no joy.

Called EI and, after confirming my make and model plane said to "bypass the Left side P-Lead Filter on the firewall". Did so with temporary wire run through the driver side window from P-lead stud on SIM to L stud on mag switch. Success! Tach works on Left, Right, and Both. Now to make the test setup permanent...

Suggestions, please. Need to remove or bypass the left side of the two filters (They look like old capacitor cans to me). Can they be individually removed? Should I simply grommet and and pass a heavy gauge wire through the same position with a dab of fire-resistant seal in the hole that will be left ? The signal from the SIM is a 60 VDC pulse at twice per rev.

Thanks,
Subsonic

[Gilbert Pierce]

I bypassed both of them on TriPacer with Bendix mags with no I’ll effects.
I ran new P-leads direct from the mags to the ignition switch.

[Subsonic]

I bypassed both of them on TriPacer with Bendix mags with no I’ll effects.
I ran new P-leads direct from the mags to the ignition switch.

Prophetic: We did almost the same. Only, we only did it on the left side. That is, the side with the new SIM. We ran a continuous shielded 18 ga wire from the left mag (SureFly SIM4P) P-Lead output stud to the L side of the Mag switch. Grommets for the firewall pass-through and Faraday cage box thing..of course.

We also ran the shield from the shield ground of the SIM to the Shield stud on the mag switch. Retained all right side hardware and electrical bonded shields as previously existed. Works perfect.

Previously installed EI R1 Digital tach displays RPM on all settings, R, L, and Both. I left the right side firewall filter in place for the original right mag. It worked, so I didn't change it. Taxied around and did a couple full run ups and mag checks. Did partial EMI test. Radio works. Will check it out robustly, tomorrow. All good so far. Fly tomorrow. Need to start practicing for spins....

Note: Another well respected A&P asked why I didn't just disconnect the old leads at each end and run a new shielded wire through the other available firewall hole. I replied, "my solution eliminated another spider web piece of junk wire that someone will have to figure out and deduce that it's not required, and, I'm lighter now." Every ounce as they say...

He shrugged. I like my solution.

-Subsonic