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Thread: An In-circuit Car Fuse Tester

  1. #1
    Supporting Member rgsparber's Avatar
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    An In-circuit Car Fuse Tester

    If you need to find a blown fuse in a car's fuse box, there is nothing wrong with pulling each fuse, testing it with a continuity tester, and, if good, re-installing it. Nothing wrong, except that it is time consuming and avoidable.

    This in-circuit fuse tester will find the bad fuse without pulling it except for one failure mode. This situation is covered by pulling the fuse.

    If you are interested, please see

    https://rick.sparber.org/InCircuitFuseTester.pdf


    Your comments are welcome. All of us are smarter than any one of us.

    Thanks,

    Rick

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    Rick

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    Altair (07-19-2019), baja (07-19-2019), Jon (07-25-2019), Paul Jones (07-18-2019), raceman61 (07-22-2019), Seedtick (07-18-2019)

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    Supporting Member mklotz's Avatar
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    Ok, Rick, now this is getting weird. As with your previous post, when I click on the URL pointing to your PDF, nothing happens. I went to your web page (https://rick.sparber.org) and tried clicking on a few random PDFs in the Car section and same thing - nada. Turning off my ad-blockers and Malwarebytes doesn't help. I checked my PDF viewer (Foxit) on other PDFs and it's working fine just as it always has.

    In the past I've had no difficulty viewing your submissions so this is very surprising. Like you, I would like to hear if others are having problems so I can determine if the difficulty is at my end or somewhere else.

    UPDATE:

    Apparently the problem resides in the forum or in Firefox. I tried your URL, but not via the forum, in Internet Explorer and it works fine.
    Last edited by mklotz; 07-18-2019 at 12:36 PM.
    ---
    Regards, Marv


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    Link works fine with Chrome also.

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    Paul Jones (07-18-2019)

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    Worked for me too (Chrome).

    Seems like the same thing I do with a common test light and only one hand.

    Clip to ground, touch pointy probe to fuse terminal. Hot side lights tells me the circuit is live, load side lights tells me fuse is good. If I don't know which is which and neither lights, circuit isn't active (or bad ahead of fuse, etc). If only one side lights, the one that didn't is the load side, and the fuse is bad.

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    Paul Jones (07-18-2019)

  8. #5
    Supporting Member VinnieL's Avatar
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    A test light or digital voltmeter works very well. The two terminals of the fuse are available on the top of hte fuse. You don't even have to remove the fuse. Just touch the two probes to the two terminals on top of the fuse. If there is NO voltage there (or test light does not light) the fuse is good. If it lights or you detect voltage the fuse is blown. Technically you are reading a voltage drop. It there is a 13-14 volt drop the fuse is shot and needs replacing.

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  10. #6
    Supporting Member rgsparber's Avatar
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    Quote Originally Posted by VinnieL View Post
    A test light or digital voltmeter works very well. The two terminals of the fuse are available on the top of hte fuse. You don't even have to remove the fuse. Just touch the two probes to the two terminals on top of the fuse. If there is NO voltage there (or test light does not light) the fuse is good. If it lights or you detect voltage the fuse is blown. Technically you are reading a voltage drop. It there is a 13-14 volt drop the fuse is shot and needs replacing.
    And if there is no voltage on the input and the fuse is blown?

    Rick
    Rick

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    Thanks rgsparber! We've added your In-Circuit Car Fuse Tester to our Testers category,
    as well as to your builder page: rgsparber's Homemade Tools. Your receipt:




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    Sorry, but I'm confused. As a tech and shop owner for over 35 years that's hard. Fuses are easy. Use a test light. Wire to ground, probe to fuse. If your probe lights up on both sides, fuse is good. If probe lights up on one side, fuse is bad. That's the easy part. If probe does not light up on both sides, make sure that circuit is powered up. If a fuse shows ok but circuit is still not powered up then you have another issue. Start checking the fuse contact first as they do corrode. After that the fun begins.



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