Welcome! Please use the navigational links to explore our website.
PartsASAP LogoCompany Logo Auction Link (800) 853-2651

Shop Now

   Allis Chalmers Case Farmall IH Ford 8N,9N,2N Ford
   Ferguson John Deere Massey Ferguson Minn. Moline Oliver

Restoration & Repair Tips Board

How to test a coil?

Welcome Guest, Log in or Register
Author 
Gwiz

02-17-2007 15:00:04




Report to Moderator

Can someone tell me how to test an ignition coil? When the ignition switch is on, I have 12 volts to the positive side of the coil. How do I test that there is fire coming out of the top and going to the distributor? I have no fire at the plugs, but I would like to see if my coil is good before blaming the points. Thanks
James




[Log in to Reply]   [No Email]
John T

02-25-2007 17:23:40




Report to Moderator
 Re: How to test a coil? in reply to Gwiz, 02-17-2007 15:00:04  
G Wiz, An ohmmeter can show if a coil is definitely BADDDDD D but cant tell you if its actually GOOD. The low voltage primary winding as measured between the lil + and - terminals should be somewhere around 1 to 4 or so ohms, depends on if 6 or 12 volt coil BUTTTTT TT if its an OPEN circuit its bad/open. The high voltage secondary winding (out the tower) should be several thousand ohms and again if its open its bad. HOWEVER even if both the priamry and secondary are continuous circuits n not open that dont necessarily measn its good cuz it can break down under operating temperature at high voltage!!!!! !!!!! i.e. if either winding is open its definitely bad, but even if it passes dont mean its good under actual high voltage and hotter operating conditions.

If you apply coil voltage across the primary lil + and -/ground terminals so the primary draws current and then you interrupt the current flow such as when the points break open, a high voltage develops at the HV terminal/tower which should arc jump a current spark across a plug gap (between HV tower and ground) or an artifical one such as a gap in the wire. You can jury rig such a coil test on the bench using a battery and a coil and jumper wires and a spark plug. The spark will be weaker since theres no condensor used but if the coil is any good at all she should still spark when current is appled then interrupted.

John T

[Log in to Reply]  [No Email]
old

02-17-2007 15:13:46




Report to Moderator
 Re: How to test a coil? in reply to Gwiz, 02-17-2007 15:00:04  
Easy way to test it is remove the wire from the points side and ground it. The remove the wire from the ignition side and turn the key on. Tkae the loose wire from the ignition and touch it to the coil and take it back off again you should have a spark from the coil wire if not you have a bad coil. I hope you understand what I'm saying here you just touch the wire on and off fast as you can to get the spark

[Log in to Reply]  [No Email]
dan hill

02-21-2007 02:13:29




Report to Moderator
 Re: How to test a coil? in reply to old, 02-17-2007 15:13:46  
Problem is with this method the condenser is out of the circuit and you will get a weak spark.Heres what a Model A ford taught me over 50 years ago.Turn the distributor until the points are open.Turn on the ignition and short the points quickly with a screw driver.You should get a nice blue spark from the high tension lead of the coil to ground.I used this method to bench test a 9n distributor and found the rotor was leaking to ground.The spark will occur when the short is removed.

[Log in to Reply]  [No Email]
old

02-21-2007 08:49:44




Report to Moderator
 Re: How to test a coil? in reply to dan hill, 02-21-2007 02:13:29  
Dan, your sort of correct but he asked about testing a coil and what I said will work to tell you if the coil is good or bad. Now ya it will not have the brite blue spark that way but it will test the coil and tell a person if its good



[Log in to Reply]  [No Email]
Gwiz

02-17-2007 15:43:29




Report to Moderator
 Re: How to test a coil? in reply to old, 02-17-2007 15:13:46  
I think I understand all but the part about grounding the points side. In this case, the negative side of the coil is to the points. Do I need to ground that side of the coil or just remove the wire from it? James



[Log in to Reply]  [No Email]
Gwiz

02-17-2007 15:48:32




Report to Moderator
 Re: How to test a coil? in reply to Gwiz, 02-17-2007 15:43:29  
OK, I think I get it. The negative side is grounded during operation as the grounded side of the points? So I do need to ground the negative side as I perform the test.
Correct?
James



[Log in to Reply]  [No Email]
old

02-17-2007 17:59:07




Report to Moderator
 Re: How to test a coil? in reply to Gwiz, 02-17-2007 15:48:32  
Yep thats a simple no high teck stuff needed test for a coil. I used it a long time ago to zap friends in school but it also works to test a coil.



[Log in to Reply]  [No Email]
[Options]  [Printer Friendly]  [Posting Help]  [Return to Forum]   [Log in to Reply]

Hop to:


TRACTOR PARTS TRACTOR MANUALS
We sell tractor parts!  We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]

Home  |  Forums


Copyright © 1997-2023 Yesterday's Tractor Co.

All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy

TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.

Yesterday's Tractors - Antique Tractor Headquarters

Website Accessibility Policy