Today we’re going to talk about the basic procedure of diagnosing an electrical problem. Sometimes, something in your car won’t work and you need to determine why. In most cases it’s either an electrical supply problem of some kind or the component itself doesn’t work. The component itself we will refer to as an electrical load. For instance, a light bulb is a load. A motor could be another load as well. On the first step that you’ll do in these circumstances is actually go to the load and find out whether you’ve got power there. Some cases you’ll check the fuses first, but it’ll depend on the accessibility of the load. In this case, the load is pretty easy to get apps and we’re going to check that first. What we’ll do is we’ll take a typical automotive test light and hook it in parallel with the load to determine if there is the presence of both battery power and ground.
In those case, I can see where the wires come in and a light circuit like this is pretty simple. We’ll first take and hook it up to growl lead on one side and the first side on the other and it won’t make our test light up. That’s an indication that there’s something missing so we need to determine what it is that’s missing. In this case, a tool is hooked up to the battery directly so we can determine if we have power on or off.
We have ground on the ground wire. That’s an indication that we do not have a battery positive, so we need to check upstream. In this case, we need to check the fuses are next step process is actually the check the fuses in the car as I remove the top of the fuse cover to gain access to the fuses inside. I’ll demonstrate in this case this type of a fuse has two little test ports where we can check and see what we have for connection.
After checking the fuse for the suspect’s circuit, we find a bad fuse. So if we remove that fuse and take a look at it, we can see that there is actually a missing gap of fuse. A fuse is designed to melt when too much current flows in a circuit. That appears to be what’s happened in this situation and in this case, we’ll get another fuse reinserted.
Now there are battery positive on both sides of it, and the trunk light is working properly again.