Lights Fans Radio Not Working in Your Car How Electric Circuits Work

In this video, I'm gonna show you how a basic circuit works and how to test it with a test light.

This is a very basic circuit. This is how most of the components work in your car, basically like a headlight switch, or even like a turn signal switch, or even your brake light switch, just very simplified. We have a battery with the positive side and the negative side. On the positive side, you have the wire, it's gonna go to a fuse, which would be in your fuse box, and then it's gonna go to the light. On the negative side, we're gonna have a wire that goes to a switch, and the switch is gonna go to the other terminal on the light.

To make the light work you need two things, you need power and ground. The ground side is the negative side, and the power side is the positive side. In everything in your car, the red wire is gonna mean the positive or the power side, and the black wire is gonna be the negative or the ground side. To make this circuit work, we need to flip the switch on. So, now we have battery negative or ground, and battery positive going to the light bulb.

If your light's not turning on and you have an electrical issue, whether it be a light or something else in your vehicle, the best place to start is the fuse. Take a look at that and see if it's blown. One way to test it is just take the fuse out, take a look and just see if it's blown. There's a little U shape in there, sometimes it's a Z and it needs to be connected. And you might even see a little burn mark like you can see in this one.

Another way to test the fuse is with a test light. Take your test light. This end is going to go on battery negative or ground. And before you even test anything, just double-check your test light, make sure it works, and it does. When testing a fuse, there is contacts on the top of the fuse. Take the other end of the test light and just touch the contact, and the light worked, but that doesn't mean the fuse is good. You go to the other side of the fuse and make sure it lights up as well. And it didn't light up, so we know that that fuse is blown. And how it should look is like this, positive on one side and positive on the other.

If the fuse is blown, it doesn't mean the fuse was just a bad fuse. Fuses don't blow on their own. There's a reason why. Something in this circuit from where the fuse is to the light bulb could be contacting a ground, and that's gonna cause the fuse to blow, or the amount of draw that the light bulb is putting on the circuit is too much, and that's gonna cause the fuse to blow as well. So, let's backtrack. If the fuse was good, let's test the wire from the battery all the way to the bulb.

So, we take the test light and test the circuit right here. And if the light comes on, then this wire all the way from the bulb back to the battery, through the fuse box is good. So, if everything checked out, now we have to test the ground side. And how we can do that with the test light is take this lead and move it to the positive side of the battery. Double-check, make sure it's lighting up. And then we can go over to the light and check the ground side. And it's not lighting up. So, that would mean something in this circuit is not connected. The reason why that wasn't lighting up, is the switch wasn't on.

So, make sure when you're testing a circuit that you're actually clicking the switch or adjusting whatever actuates the light bulb. If we're testing this circuit and the light does not light up as we push the button, then there's something wrong on this ground circuit. If we test the switch right here with the test light and activate the switch and the test light does not light up, as long as there is a ground on this side coming into the switch, like that, if we have the ground coming into the switch, but when you toggle the switch, it doesn't come out, then the switch is gonna be bad.

Another way to test the switch would be to disconnect the two wires and jump them together, which is making a circuit, closing the circuit just like that. If you still didn't have a good ground at the switch, you would wanna check the wire that goes to the ground. Either the ground on the battery or the ground on the chassis of the vehicle. Sometimes something as simple as a light bulb circuit can be hard to diagnose. I hope this simplified it for you and you enjoyed this video. If you did subscribe to our channel, ring the bell, turn on all notifications, so you don't miss any of our videos.