So I’m not that good at wiring but I been following danner on YouTube and when he shows how to test for power with a basic test light he also puts it to a ground without moving from the negative post….and when he test for ground if it don’t light up he says it’s a good ground….my question is what about if the ground wire is broke some were? Or is that assuming the ground wire is not cut in half somewhere? I know to put the test light to positive to test for ground so the light will light showing you have a good ground but how would you know if the ground wire is not broke the danner method? Any help is appreciated danner is super smart so a lot of his test are over my head lol
It really does not make sense but it happens. The same thing with a volt meter. A ground to ground test with a bad ground will show voltage. I think the theory is something around this line: essentially the ground wire is flowing some amount of voltage and current from positive to negative, when you have a bad ground, all of the electricity can not flow through the ground wire to ground and remains on the wire thus why the test light would light up. However you have to be careful where you do you testing. If you have a broken wire, the point where that wire connects, and any point before the break would look good, but any point between the component and ground would have voltage.
I'm not a trained mechanic but my understanding of it is that on a good circuit there's only one big source of resistance which is the load, so on a good circuit all the voltage gets dropped across the load. If all the voltage gets dropped across the load there's 0V left on the ground. In that case if you put your test light on the negative battery post and touched the other end to the ground wire the test light would have 0V on both sides so it wouldn't come on.
If there's a bad ground it means there's a second resistance in the circuit, so now some of the voltage gets dropped to across the load and some gets dropped across the second resistance. Say 8V across the load and 4V across the second resistance. Now if you put your test light on the negative battery post and touched it to the ground wire there would be 4V on one side of the test light and 0V on the other side so the light would come on dim showing a bad ground.
If the ground wire was fully broken there would be an open circuit. Open circuit mean no current flow. No current flow means no voltage drop across the load. No voltage drop across the load means all the voltage would show up across the open on the ground wire. In that case if you touched the test light to the ground wire it would light up brightly because the test light would be the only path to ground so all the current would flow through it. Not sure if that answers your question but that's my understanding of what's happening.
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