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How do i check the trigger side of the coil with a test light? can you send me a wiring digram?

1975 Ford F350 360 engine there is voltage at the + side on the coil but i didn't check the - side how do i check the - side? there is know spark at the secondary coil wire.

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On a standard external coil, you can use an incandescent test light. ground the test light lead. key on engine off both terminals of the coil should be HOT (light on when you touch either). If the ground is being sent by the module (or PCM on cars where the module is part of the main computer), then when the engine is running or cranking, the light should FLASH if you are holding it to negative while the engine is cranking or running. (Note, it will flash very fast when the car is running, so fast it may look solid if you dont look very carefully). That flashing is the trigger signal pulse grounding the coil to fire it for each cylinder. That in itself is only 1 test, you wont know if its enough ground, too long or short, or if the coil is functional. Its a very simple test using the cheapest of equipment. Proper testing using better equipment will tell you alot more info. But that will tell you if your ignition module is trying to fire the coil. Other issues like crankshaft sensor, theft system, or ignition switch crank-only outputs can cause no spark cranking and are harder to diagnose.

Posted on Jun 26, 2018

  • Joe Russell Jun 26, 2018

    i am working on a 1975 Ford F350 360 engine 1t have a ignition module, pickup coil i don't think it have a computer and crankshaft sensor do the ignition module fire the coil or the pickup coil fire the coil ignition? i hope you can help me find out why there is no spark at the ignition coil second wire and spark plug wire. will a timing chain cause no spark?

  • Robert Wood
    Robert Wood Jul 09, 2018

    The ignition module is a computer .


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Check for voltage at the negative (-) side when the positive (+) side has power. There should be voltage on both. If not, you have a bad coil

Posted on Jun 24, 2018

  • Joe Russell Jun 26, 2018

    There is voltage on both side of the coil i check for a trigger signal on the (-) side of the coil with a test light i connect the clip end of the test light to the (-) post on the battry and the pointer end of the test light to the (-) side of the coil and crank the engine look like the test light was blinking did i hook the test light up right? i hope you can help me find out why there is no spark at the coil secondary wire. what i need to do next to fix the problem?

  • T Wolgamuth
    T Wolgamuth Jun 26, 2018

    If you hold (or prop is better so you don't get shocked) the center coil wire close to grounded metal (within 1/4") (or just plugged into a grounded spark plug) and turn motor so that the light is blinking as you did above, you should be getting a spark every time the test light goes out. If it's blinking and your not getting a spark, you have a bad coil. Can't think of what else it would be.


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A test light clipped to battery positive and the probe tip touched to ignition coil negative while cranking the engine over will blink if receiving pulse signal .

Posted on Jun 26, 2018

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Posted on Jan 02, 2017

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SOURCE: engine shut off while driving, cranks over.

Hi, I had the same problem, no spark. I check coil it was good, check the injectors for pulse they are fine, I checked the four wire harnes conected to the distributor are fine, I check resistance at the power transistor in top of the air filter assembly and it was wrong, I just replaced the power transistor and the car is running good again.
I hope this help you.

Posted on Oct 21, 2008

  • 5821 Answers

SOURCE: Check engine light will not come on when key is

bring coil to parts place and testit--get car scanned by mobile mechanic

Posted on Oct 20, 2010

  • 547 Answers

SOURCE: I have a 1995 jetta

This sounds like a bad crank position sensor. The crankshaft position sensor on the AAA engine is located on the "intake" side of the engine block, near the flywheel. Pull that sensor out and see if Auto Zone has a test procedure for it. There is also a chance your ECM fuse is blown. If your service engine soon light comes on when you turn the key on (not starting it) then the fuse is good.

Posted on Dec 05, 2010

  • 5332 Answers

SOURCE: Weak or no spark - won't start.

If the coil cannot produce enought spark to jump at least a one inch gap, replace it. Is the coil internal or external to the distributor?

I’m happy to assist further over the phone at

Posted on Aug 05, 2012

  • 5204 Answers

SOURCE: why there is no spark from the coil wire when cranking why?

If you hook a test light to battery positive and touch negative terminal on coil and crank engine over does light blink ?

Posted on Jun 22, 2018

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