The electrical wiring in a car is a system of color-coded wires called the loom. Where several wires run side by side they are bound together with insulating tape or plastic sleeving.
Several modern cars have separate thin wires embedded in flat plastic strips. These strips are very compact, and are used mainly for accessories and relay controls that require little power. Wires and bundles of wires are clipped to the bodywork to keep them out of the way. Where they run through a hole, the sharp edges are lined with a rubber grommet.
Sometimes the loom is split into sections joined by multi-pin plugs and sockets, in order that it are often removed and refitted section by section. Joins in individual wires are usually made with crimp connectors. the color on the sleeve of a connector denotes the size of wire it’ll take.
The bared ends of every wire are pushed into opposite ends of the metal-lined plastic sleeve, and squeezed with crimping pliers. There are multiple sleeves or other special connectors where a wire branches off. Wires are usually connected to components by plastic-covered terminals which push on to a blade on the unit called a spade terminal.
Nearly all kinds of terminals should be fitted to the wire with crimping pliers. There are a couple of types like the `Scotchlok’ which are secured by clips. For additional security, you’ll add solder to the wire. Use a 25-65 watt iron for many work, and a 150-250 watt one for giant cables, or an 8 oz (225 g) gas-heated iron.
Disconnect both terminals of the battery before doing any work on wiring aside from testing. Whenever you’re employed on the car, watch for any a part of the loom coming loose from its clips, for there’s a risk of it getting trapped or burned. Always replace wiring in its clips.
Also look for grommets that have begin of their holes. The sharp edge of the opening will soon chafe through wire insulation and cause a brief circuit. Whenever you pull a connection apart, search for corrosion which could cause bad contact. If necessary, clean contacting metal surfaces with a fine file or emery cloth. But it’s better to replace the terminal once corrosion has destroyed the surface coating.
Making repairs to the loom
The wiring loom itself seldom goes wrong, but after other repairs are made, a cable could also be trapped and its insulation cut through, causing a brief circuit. If this doesn’t blow a fuse the wiring overheats and melts insulation, perhaps starting a fire. an identical result can come from fitting accessories incorrectly, or if power demand is just too high for the dimensions of the wire getting used.
After a few years , insulation may become hard and brittle, particularly where it’s exposed to heat, as within the engine bay. Sections, or all of the loom, may have replacing. The damage caused by overheated wires is straightforward to find; but if only one wire has overheated and melted at some point, you’ll need to use a circuit tester to seek out the break. If the damage is in an open run of wiring, you’ll be ready to mend separate wires without removing a section of the loom. If it’s in any a part of the covered sections, you would like to get rid of a minimum of a part of the wiring loom.
Before you disconnect anything, make absolutely sure you know the way to put it back. Number each side of each connection with labels made from masking tape. If necessary, make drawings of cable routes and the way clips fit. Use a craft knife or razor blade to chop away the wrapping from the damaged section. lookout to not dig the plastic cable insulation. Even if just one wire has overheated, inspect all the others to form sure their insulation isn’t damaged.
Before cutting out damaged wires, make sure that the color coding is that the same at each end of the damaged section of every wire, which it’s not so discolored that it’s unrecognizable. If there’s any chance of confusion, label both ends. Cut out all the damaged wires with wire cutters. opened up the cuts across a bundle of several wires: if many joins are opposite one another their bulk may make it difficult to suit the loom into the car.
If possible, replace wiring with new wire of an equivalent color. The new wire must be the proper size: there are five sizes, counting on current rating. Repairs in wrapped sections of the loom are the sole places where you’ll join wires by twisting them together and soldering the joint mainly because there might not be room for the other method. If possible, use an insulated in-line crimp connector.
Test each mended wire with a circuit tester and battery, connected to the nearest connectors either side of the mend. Re-wrap the exposed section of the loom with self-adhesive or ‘clingfilm’ PVC insulating tape. Put some layers between the exposed section and adjoining wires – not merely a cover over the top – then fit the loom back to the car. Reconnect all terminals and clips, then test all the electrical components involved. If an outlying a part of the loom with few wires has been damaged, it may be simpler to replace each wire to the top of the loom rather than inserting a section. If so, use the old, damaged wire as a guide to the length of the new. In an open area of wiring, join old and new with snap connectors.
Fitting new wiring
When you fit accessories you must use large enough cables. As far as you’ll , route the new wiring along the course of the existing loom, using an equivalent clips and grommets. Push a screwdriver blade through the grommet carefully to enlarge it for the new cables, taking care to not damage insulation on existing wires.
If you pass a cable through a new hole, fit the opening with a grommet. To pass wires up door pillars or behind trim, tape them to a bit of fairly stiff wire, poke it carefully behind the trim or up the pillar, and pull it through at the far end, bringing the wire with it. Use insulating tape in a spiral to bind wires together.
If you have to lead a new wire along a difficult route – to the rear of the car, for instance – you’ll take the chance to steer a spare wire at an equivalent time, for any accessory you would possibly want to suit later. Cover the top of a spare wire with friction tape to stop an electrical short circuit.
Identifying cable sizes
Cable sizes are given by two numbers. The first one is the number of strands. The second (which is always the same in car wiring) is the diameter of each strand in millimeters.
Twisting wires together and fitting spade terminals
To connect two wires, use a wire stripper to remove about in. (19 mm) of insulation from each wire. Twist the bare ends together, then use pliers to press the twisted section into a compact shape. Solder the wires together so that they can’t be pulled apart, using only a little solder to avoid making the joint bulky.
Wind insulating tape in a spiral over the joint. To fit a spade terminal, slip the insulating cover over the wire and push it up the wire, out of the way. Use a wire stripper to remove about 1/8in. (3 mm) of insulation from the top of the wire. Lay the bare strands within the inner section of the connector. Use crimping pliers to tighten the 2 small tongues firmly round the insulated a part of the wire.
On the opposite side of the connector, push the wire strands back and down flat. Hold the connector blade upwards to avoid solder running into the spade part. Solder the wire to the connector with only enough solder to secure all the strands. Let the connector cool before sliding the duvet back.
Fitting a bullet connector
Use a wire stripper to remove about 3/8 in. (10 mm) of insulation from the top of the wire. Push the wire into the connector so that the strands just protrude from the round end. Grip the cable, connector uppermost, in a vice or self-locking pliers, so that the connector rests on top of the vice and can’t slide down the wire when soldering.
Apply solder on the top of the connector, and let it melt and run down inside. Trim off the protruding strands with wire cutters.