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Wiring at the magneto...

Michael Burbidge

Michael Burbidge

Well Known Member
My engine has slick mags. I've looked around a bit and cannot find information on which terminals on the mag are for what. I understand and have read the information about how to wire the mag to the switch, etc. I just don't know which screws on the magneto are for ground and which for the p-lead.

Here's a picture of my magneto. I've labeled each of the screws with what I think they're for.

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I'm guessing the nut with the fabric washer is where I connect the p-lead. I've labeled that P-Lead. The screw marked GND is actually marked GND on the magneto. I'm guessing that is ground and where I would wire to ground on the mag. The one that confuses me is the one which I've labeled "Unknown". What is that for?

The screws appear to be torx drive. Do you happen to know what size?

Thanks for the help,
Michael-
 
Mag Wiring

Michael, your UNKNOWN is just a vent cap, nothing goes there. Assuming you have a shielded wire, you can use the ground to ground the end of the wire shield.
 
Securing p-lead...

Thanks.

One more question. Sometimes I'm not sure how to secure a wire firewall forward. This is one of those times. These are no other wires in the near vacinity to help secure the p-lead. Here's a picture. It seems like that 20 awg wire would break after awhile. Suggestions?

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Michael-
 
Wire support

Hard get a "perspective", but it looks OK. You might use shrink wrap around the leads to provide more flex support. I didn't use anything less than 18ga because of support reasons and the ability to get a good crimp on lug connectors.
 
Looks okay.

A good idea to leave some slack for the engine to move a bit in the mount without tearing everything apart.

Dan
 
Switch

Remember when wiring the magneto to a switch, off or open on the switch will be ungrounded at the magneto, and thus the magneto will be hot. On or closed at the switch will allow the magneto to be grounded and not producing spark. I made that mistake initially.
 
Unknown Vent

The unknown Vent port can be used to hook up a fresh air hose.
Rather than just direct a hose onto the housing of the magneto, take the cap off and direct the cooling air right into the magneto where it does the most good.
If you remove the cap you will see a nut of sorts with 6 holes in it.
I removed this nut drilled out a hole large enough to accept a pipe nipple that would accommodate the inside diameter of a fresh air hose from the top of the engine plenum.
The pipe nipple is simply glued in with JB weld.
This magneto cooling idea is something that everyone seems to do at my airport. While most builders install some kind of air hose directed towards cooling the magneto, I think most of those are not very effective.
 
Mag

There is no demonstrated need for external cooling air to the mag. It IS a good way to get water inside the mag.
 
That hole is actually where you screw in the mag-lok tool that locks the distributor gear during assembly and mag installation. If you expanded the hole you can't ever use a mag-lok again. I suppose now you can stick your finger in there and be a human mag-lok.
 
Pressurized mags also use this hole connected to upper deck air but that air is filtered by the induction filter and a cartridge filter before it gets into the mag. I agree putting unfiltered air into the mag is asking for a mag failure.
 
aerhed said:
That hole is actually where you screw in the mag-lok tool that locks the distributor gear during assembly and mag installation. If you expanded the hole you can't ever use a mag-lok again. I suppose now you can stick your finger in there and be a human mag-lok.
Click to expand...

Err... isn't that only for Bendix mags?

The original picture was a Slick....

Slick uses one of these...

854048934_125.jpg
 
Last edited:
Michael Burbidge said:
Sometimes I'm not sure how to secure a wire firewall forward. This is one of those times. These are no other wires in the near vacinity to help secure the p-lead. Here's a picture. It seems like that 20 awg wire would break after awhile. Suggestions?
Click to expand...

Good for you Mike. Too often mag wires are just left flopping around back there. Some percentage eventually self-disconnect, and then somebody has a live prop.

Use the ground screw to secure both a plain steel adel and the ground wire ring terminal. I don't recall if you'll need a slightly longer screw:

2lcphl4.jpg
 
Last edited:
Al, duh. Sorry, had bendix on the brain. There's still a red mark to look at in there though isn't there?
 
Umm;
An air cooling port won't work unless there is an exhaust port to let the 'hot' air out.
Also what jsr14855 and aerhed said above reguarding water and dirt.
 
DanH said:
Good for you Mike. Too often mag wires are just left flopping around back there. Some percentage eventually self-disconnect, and then somebody has a live prop.

Use the ground screw to secure both a plain steel adel and the ground wire ring terminal. I don't recall if you'll need a slightly longer screw:

2lcphl4.jpg
Click to expand...

Thank you Dan. Great solution for the question. Somehow the thread drifted and you brought it back on track. I was following this thread because I was also concerned for my installation.
 
jrs14855 said:
There is no demonstrated need for external cooling air to the mag. It IS a good way to get water inside the mag.
Click to expand...

Are you saying there is no need for blast air from the top side to cool the magneto, or just saying there is no need to open up the magneto and send the air right into it?
 
He's saying that you don't want to inject air directly into the mag. Some mag installations stay plenty cool without blast tubes, some don't. A tube blowing onto the outside of the mag can't hurt but does rob a little cooling air from the engine and provides a path for rain water to hit your accessories (which I've never heard of a problem with).
 
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