What is a short circuit? A short circuit is a connection of two points (wires) having different potentials (plus and minus) which should not be in normal operation of the device. We are talking about a car (motorcycle, ATV, snowmobile) so consider ways to find a short circuit will be for the car. The article is designed for novice electricians and advanced car owners, if you do not know what a multimeter, it is better to contact the service, it will be faster and cheaper, in the end everyone should do their own thing. In the article there are several invented examples of short circuit search and links to real examples of finding and eliminating circuits in cars from my practice.
As you know all electrical circuits in the car (with the exception of the power circuit of the starter) are protected by fuses. A short circuit will always cause the fuse protecting this circuit to burn out and there is nothing wrong with the circuit itself. The danger arises when people do not understand the cause of the combustion of the fuse replace the fuse with a larger nominal value, or put fuses of incomprehensible production. Such fuses are made of who knows what and may not burn at all.
To search for a short circuit, we use an electrical circuit, a multimeter, it happens that we use a light bulb as a tool. Wiring find now is not a big problem, in the simplest cases, you can do without the scheme, I advise you to look at the electrician scheme always, to improve their skills.
For example came to us the Nissan Qashqai with the inoperative heated mirror. First of all, check the fuse heating mirrors in the cabin fuse box, it is serviceable, check whether there is power on it when you turn on the rear window heating, no power. Look scheme.
The mirror fuse is located in the cabin fuse box. And in the IPDM block there is a relay of inclusion of heating of back glass and mirrors and two fuses included in parallel on 15 amperes. Nissan always puts two fuses in parallel. Check the fuses, burned out. Our task with minimal time and minimal disassembly of the car to find and eliminate the circuit. The weak point in this case is corrugated, the transition from the body to the liftgate to open and view it a couple of minutes, watching the entire wire. Next, you need to possibly with the least disassembly of the cabin to determine the wiring section on which there is a short circuit.
We have excellent access to the mirror fuse, from it and start measuring. Take out the fuse to the circuit to measure mirrors and a multimeter in the ohmmeter mode, measure continuity or resistance
Suppose a resistance of 0.5 Ohm — short circuit is present. Next, you need to decide in which part of the wiring to look for this short circuit, according to the layout of the connectors, we will find where the connection E101 — B11 is located.
The connector is conveniently located, you only need to remove the sill plate and kick panel. Disconnect the connector and make a measurement of resistance on both sides of the connector.
Suppose a short circuit in the part of the wiring that goes to the back of the car. The wires in the corrugation we have already checked at the beginning, there are no more connectors, so it remains only to disassemble and look. Damage to the wiring is almost always visible, remove the rear sill trim and see the damaged wires and the consequences of body repair.
Recommend pursue regularly such coaching received, open scheme any car, come up with fault and ways its diagnostics and eliminate, podnaberetes experience in reading wiring diagrams and search for malfunctions. The time spent will definitely pay off when repairing real cars.
one more method
Also, auto electricians often use an ordinary incandescent lamp when searching for a short circuit. In this case, instead of the burnt fuse in the circuit connect the lamp, I usually use H4, a lot of them lying around with the burnt thread of the dipped beam.
For example, we have a MMC Pajero 4 with broken reversing lights and a burning fuse. You can search for a fault as in the previous case, but it will be easier and faster to connect the lamp instead of the fuse, turn on the ignition, reverse gear and this lamp flashes in full glow, and the reversing lights are not. This means that there is a short circuit in the reversing lamp circuit. Our lamp limits the current in this circuit, it will not be more than what the lamp consumes and at the same time serves as an indicator that a short circuit is present.
At the same time, we immediately note that the lamp lights up only after we turn on the reverse gear, that is, in the area from the fuse to the gear selector, there is definitely no closure (and there are, by the way, two connectors and branches, not a little cut off). Next, go and disconnect the connectors from the rear lights. The lamp continues to burn, that is, the circuit is not in the lanterns. Forth, acting from simple to complex, climb under machine and find on box connector selector transmission Since-05 (suppose have us machine gun).
And we begin to actively move the wiring on the box, while we see that our lamp began to flash, that is, the circuit disappears, then everything is simple, we find the place of damage and repair. It will look something like this