Coil Polarity

Bob Grieb

Bob Grieb

Senior Member
I cannot find a diagram in the Les Andrews Manual that reflects the proper polarity for installing a coil. Does polarity make any difference?

Thanks

Bob
 
There are two ways to accurately determine coil polarity. The first is a device sold by most Model A suppliers. It plugs into the top of the distributor cap and has two LEDs that indicate correct of reversed polarity. I bought one from Bratton's years ago and checked all the Model A's at a club gathering and found about half reversed. When we corrected them the owners could not tell much difference. I believe the reversal robs only a few horse power.

The second method is the favorite of 9th grade auto shop teachers. You insert the tip of a lead pencil into the spark as it jumps from ground to one of the leads. It will flare on one side. If I remember correctly it flares on the ground side if the polarity is correct. After the teacher demonstrates this he usually hands the pencil to some kid, usually the class pain, and has him try it.

Tom Endy
 
I just bought one about three weeks from brattons that Tom is talking about. Checked my two model a motors and my flathead. A simple tool that works.
 
Am I missing something or don't you just attach the power to the negative terminal and the distributor to the positive on a positive ground wired car?
 
Kirby1374 said:
Am I missing something or don't you just attach the power to the negative terminal and the distributor to the positive on a positive ground wired car?
Click to expand...

Yes, that's the way to do it if the coil is marked + and -. If the coil isn't marked, then go to this excellent posting by the Chicagoland MG club. It's a quick and complete read and tells why and when you need the correct polarity.

http://chicagolandmgclub.com/techtips/general/574.html
 
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