Electrical

For most people, the Electrical system is the scariest part of the car. All those wires, and the magical force of electricity, can be very confusing. But dry your eyes mate, we'll get you through it.

Engine

All of the main functions of the engine; the Fuel, Air and Spark, are ultimately controlled electrically.

Ignition

In this article, Ignition refers to turning the key to make the engine start. For other meanings of ignition, refer to the Ignition page.

Most of your car's electrical systems will activate when the key is put into the ignition barrel and turned. This simple switch clips onto the back of the lock barrel, and goes to a plastic connector that links the switch to the main Loom.

The wiring for the switch is relatively simple; so simple, in fact, that if very rarely causes any problems. Seven wires connect to the switch, which are:

• black/yellow - Start wire
• red - permanent 12V in
• green - Ignition circuits
• green/violet - rear demister
• violet - Ancilliaries (wipers/ lights)
• brown - seat belt warn light
• brown/blue - brake fluid warn light

The essential wires are therefore the black/yellow, red, green and violet cables. However, if your car is not starting and you are looking for faults, you can test the starter from the diagnostic plug in the engine bay.

ECU

Main article: ECU

The brain of your car, the ECU is in control of engine running. It takes readings from sensors scattered around the engine bay, and adjusts the fueling accordingly. It also governs whether the Ignition and Fuel circuits are powered, by controlling the DME relay.

Charging

Main article: Charging

To keep everything running, your system needs to generate electricity as it's used. To do that your car has an alternator, driven by a belt from the engine. The alternator is directly connected to the main distribution circuit, as well as to the battery to keep that topped and fresh.

Loom

Main article: Loom

The loom is one enormous snake of wires, and is a one-piece unit in E30s. From the very back of the car all the way to the fuse box, it feeds every primary and ancillary circuit in the vehicle, with only a small number of plug-in extras to feed things like the OBC and cruise control.

The same loom was used in all cars for any specific year, but there are small differences between years. The biggest difference is between facelift (1987-94) and pre-facelift (82-87) cars, when a large number of modifications were made to various systems throughout the vehicle. There are also important differences to Touring and Cabriolet models, since they have features not fitted to standard saloons.

If you want to know more about any particular aspect of the loom, check out our wiring diagrams.

Interior

Instruments

Main article: Instruments

Sticking your hand out of the window and wiggling it in the slipstream isn't a very accurate way of measuring speed. For that reason, your car is kitted out with all manner of dials, clocks and gauges to keep you informed of how the car is working.

These instruments are all contained in the Dash Cluster, which is fed by three main wires from the Loom. While clusters can be swapped between vehicles, they contain a special chip or Coding Plug that tells the instruments what engine is fitted to the car. Fitting the wrong coding plug will give massively incorrect readings for the instruments.

An extra unit, known as the On-Board Computer or OBC, was also available. These units good give you simple time and temperature functions, while more advanced units had access to fuel economy and range data.

Stereo

Main article: Audio

While the noise of the engine should be all you need when driving an E30, many people want some phat sounds while driving, to while away the motorway miles.

The E30 was available with a wide range of stereo head units from the factory, and all of the wiring is in place to fit four speakers within the cabin. There is also extra wiring provided for tweeter pods, which fit into the front doors.

All of the stereo wiring is a one-piece accessory loom using a standard BMW colour coding system, and isn't really compatible with more modern stereos. Because of that, most cars have had their wiring butchered and chopped over the past two decades by enthusiastic teens and ill-informed installers, so the current state of your stereo system could be a complete mystery.

Exterior

Lights

Main article: Lights

Inside and out, your car is fitted with a multitude of bulbs. While the most obvious is to provide illumination so that you can see what you are doing, the majority of them provide information on the status of your car. Understanding not only the headlights but also the instrument and check panel lights will hep you keep your car in optimum condition.

Windows

Main article: Windows

Wing Mirrors

Main article: Wing Mirrors

Locks

Main article: Central Locking

Sunroof

Main article: Sunroof

While poverty-specification vehicles came with a windy handle to open and close the roof, some buyers opted for the electric alternative. Mounted in the roof and activated with a switch above the driver's head, the motor offered two functions; upward tilt and full recline.

If you have an "exercise roof", all of the wiring should be in place to fit the electric motor and switch to upgrade your sunroof.

Rear Demister

Since the E30 is such a superior vehicle, you'll be using your rear view mirror a lot to watch the losers you left behind at those traffic lights. But in cold and damp conditions, the rear window can steam up, obscuring your view and spoiling your moment of victory. For that purpose, all E30s are fitted with a rear demister (or defogger, if you're American), to help keep the glass clear.

The demister is made up of simple carbon strips stuck to the glass, which warm up when power is passed through them. This wire lattice is powered by its own circuit, and is activated by a switch on the dashboard.

If you want to make your Demister switch glow like the Hazard and Wiper switches, then learn more about illuminating your demister switch.

Ancilliaries

Cruise Control

Main article: Cruise Control

Heated

The term Heated can be applied to a number of accessories on the E30. The list of heated features includes:

• Heated Seats
• Heated Wing Mirrors
• Heated Washer Jets
• Heated Door Locks

The main Loom provides plugs for all of these accessories in their respective locations, but there are no switches; all heated components except the Seats are activated automatically when the ignition is turned on.

If you feel the need to prepare your car for cold weather climes, then learn more about retrofitting heated washer jets.

Common Problems

Central locking: It is very common for E30s to develop issues with their central locking. This is caused by a constant live power source running through the door which, over time, causes the terminals in the door loom to corrode. This has a simple fix which all E30s can benefit from.