Now the other type of electrical problem is the short circuit. It's called a short circuit because instead of the voltage taking the "long" way through the circuit to ground, it takes the "short" way to ground. These can be a little tougher to troubleshoot. Since all the battery amperage wants to go through the wire, it will blow the fuse. This is kind of a Catch-22, you can't find the short unless there's power, and there's no power until you find the short. There's two ways to remedy this situation, the first is to buy a self-resetting circuit breaker and the other is to put a load in the circuit so the fuse will not blow. I have a self-resetting circuit breaker, and it works quite well.
I prefer the other option, putting a load into the circuit. Now I'd like to say this was my idea, but I got the idea from my Uncle who was a mechanic for over 40 years. It was so simple and elegant that I adapted it for myself and used it with great success for many years. What you need is a old fuse, a bulb and socket and two lengths of wire. They can be as long or short as you like. I took off the plastic from around the end of the fuse and soldered a piece of wire to each end. Then I soldered the socket to the other ends of the wire. I taped it up and I got a little fancy and made up a small cage to go around the bulb. Then I simply plug my modified fuse into the fuse box and there's my circuit load. Now I can troubleshoot the circuit and find the short.
In looking for a short, the first thing you need to do is look at your wiring diagram and see what is on that circuit. Then, one by one, unplug every component and look at the light as you do so. When the light goes out, you found the part that's shorting out. If, after all the components are unplugged, the light is still on then the short is in the wiring.
Now what you need to do is cut up the circuit into blocks as you did in looking for a open circuit. Look at your diagram and locate the connectors, and working from back to front, unplug them one at a time, checking the light. When it goes out, you have isolated the area that is shorted.
These two techniques will work for the home mechanic to find most common electrical problems. More advanced problems require the use of a voltmeter and ohmmeter to locate. Most service manuals you but will have a troubleshooting tree to guide you through of electrical troubleshooting. The important thing is not to shortcut the procedure. The result of one test usually relay on the validity of the previous test. By shortcutting you will invalidate the testing and will have to start all over again or give you erroneous results.
To recap, when you troubleshoot a circuit, understand it first. Use your schematics and diagrams to see how it works and is laid out. Then work in sections until the problem is found. These points are the key to successful electrical troubleshooting.
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