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10-13-2022, 06:16 PM | #15 |
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It takes way less than 12V to start a car, a starter will crank down to really low voltage, often low enough that modules are flickering on and off and a car will crank and start down in the 10V range, heck, I seen some shit start below 9V but more to the point...
We have a binary situation here, not a slow crank, a crank and then -nothing- and I presume the dash lights are NOT throwing a disco since op hasn't brought it up so his voltage isn't so low that electronics are throwing a fit. It's still better to ascertain "does car want to start by putting voltage to Switch terminal" Y/N If Yes then you've got all the time in the world to worry about supplying a lot of amps to anything you might desire, but if No, a battery connection and ground path so clean you could eat off of it will not help it start. |
10-13-2022, 10:51 PM | #16 | |
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10-14-2022, 01:30 AM | #17 | |
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Lights and gauges were completely unaffected. And just for clarification yes I mean the headlights. |
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10-14-2022, 01:32 AM | #18 | |
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When my old battery was crapping out, it would get dimmer until there was nothing left. Then I would just jump it and it would start. New battery in it now with a tender. |
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10-14-2022, 07:10 PM | #19 |
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Ok lets stop talking or recommending a test light. It is not the 70’s any more. You can get a volt meter for $15. We need to know voltage, not the light dimmed a little. Hell the price of infrared imaging has come dow so much I have one. Talk about a great way to troubleshoot electrical!!!
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10-14-2022, 11:39 PM | #20 | |
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10-18-2022, 03:34 PM | #21 | |
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As much as I hate to admit it, I have to agree with @Tcoat on this one. If you're using an old-school test light to attempt electrical troubleshooting on modern vehicles, you are not a mechanic that I would want to bring my vehicle to. A decent quality digital VOM is the proper tool to troubleshoot with in these (and all) modern cars. Throw that old test light away. Then check the battery voltage at each post first, then from the positive post to one of the +12V fuses in the fuse block under the hood that is always energized, then crank the starter and measure that voltage. This will let you know if you have any resistance between the post and the fuses. Any measured voltage greater than 0.1 volts and you have too much resistance (probably caused by corrosion or loose terminals) and you should address that. Do the same thing for the negative post and to the engine block while cranking. Any measured voltage greater than 0.1 volts indicates resistance between the negative post and to the block. Address that if needed. Once you've established that your positive and negative cables are clean and secure, and that your battery is not weak, then you can move on to diagnosing individual circuits. |
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10-18-2022, 05:51 PM | #22 | |
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The starter circuit is one of the last things on modern cars, along with a rear defrost, that is still ideal prey for a test light. If you want to think otherwise that's fine by me, enjoy yourself. |
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10-18-2022, 06:18 PM | #23 |
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Test lights have their place, especially when you are just checking if something is switching when it is supposed to. Sometimes it is not easy to manipulate a control while holding a meter leads where they need to be and be able to see the screen, even with alligator clips. I have an LED with a magnet glued to it with alligator clips on it to check switching that I use sometimes.
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10-18-2022, 09:36 PM | #24 |
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10-18-2022, 09:40 PM | #25 | |
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10-18-2022, 09:45 PM | #26 | |
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Led with magnet glued to it that I found-almost free. My old meter is still kicking. Not upgrading till I have to.
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10-18-2022, 10:06 PM | #27 | |
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usually can spot the problem in the form a greasy breaker/melted wire first.
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10-19-2022, 10:17 AM | #28 | |
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The issue is that the '72 doesn't have sub-5 volt circuits in it that could easily be damaged by connecting a 12-volt incandescent bulb in series with them. Modern cars do, and the possibility exists that when you are probing for the suspected correct circuit, you might accidentally probe one of those low voltage circuits. Then you'll have to explain to your customer why they need a new ECU when all they originally dropped their car off was for a non-start situation....and you'll still have troubleshoot and fix the original issue once the ECU has been replaced and reprogrammed, etc. And you may have introduced even more issues to some of the low voltage circuits that the ECU is monitoring even after all of that. That is a risk that I would not take as a technician with many years of experience diagnosing vehicle electrical issues, and just about any other kind of electrical issue that you can think of. For all of the old-school guys that still insist on using a "test light" to troubleshoot with, I would recommend a digital version of it such as this one here, which as you can see has sequencial LEDs to show the level of voltage in the circuit you are testing, and can conveniently allow you to have one hand free if you attach an alligator-type clamp adapter to the end of the wired probe. The low voltage electronics in the digital "test light" pose no threat to modern electronics. Using a tool like this would be insurance taken to prevent a huge headache down the road. |
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