From E30 Zone Wiki
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.
While it would be impossible to cover the entire electrical system on one page, we've managed to compile all the handy links together so that you can find what you need in just a few clicks.
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 - Ancillaries (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.
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 fuelling accordingly. It also governs whether the Ignition and Fuel circuits are powered, by controlling the DME relay.
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.
Main article: Fuse Box
All of the fuses for the car are contained in the fuse box, which sits in the engine bay against the bulkhead. It contains up to 30 fuses, and is a standard unit across the entire E30 range. For a list of fuses, learn more about the fuse box.
The fuse box itself is an integral part of the main loom, and can't be separated.
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.
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.
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.
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.
Main article: Windows
To save you pumping away at the handles, top-class E30s were fitted with two or four electric windows, depending on your body style and budget. The wiring for these means that they will work when the doors are open, or with the ignition on. A safety fuse and a cut-out button are also fitted, to prevent accidents and to disable the rear windows if needed.
The wiring for all electric windows is contained within the main Loom. If you are considering fitting electric windows, then you will only need the cabling inside the doors themselves, which will include the switch plugs and motor connections. The plugs for the switches are in place under the centre console.
Because of the the numbers of switches, motors and relays in the electric window system, there are number of ways these systems can go wrong. The simplest faults will only stop one window working, while more serious issues will prevent them all from operating under any circumstances. If you're having issues, check out our wiring diagrams or learn more about windows.
Main article: Wing Mirrors
No leaning over and adjusting the mirrors with your outstretched fingertips; E30s come equipped with electric mirrors that allow you to adjust the horizontal and vertical angle of both wingers, from one little joystick mounted on the driver's door.
Main article: Central Locking
One of the luxuries we take for granted with modern cars is not having to pull up the little plastic knob to unlock a door from the inside. E30s were no different, with central locking being a popular optional extra. Putting the key into either the driver, passenger or boot lock and unlocking should unlock all the other doors at the same time.
This is done with microswitches; little contacts that are closed when the lock barrel is turned. This sends a signal to the Central Locking module to power the actuators, which are little more than electric arms that push or pull that plastic knob up or down.
The trouble is that over the years, the system degrades. The microswitches get gunked up, the central locking module gets flooded with water (it's located behind the speaker in the passenger footwell) and, most commonly, the pins in the door loom plug get corroded, causing total system failure. Fortunately, there's a fix for this, called the Red/Black Wire Mod which all E30s can benefit from.
The central locking system also controls the petrol flap. If your locking system has failed, you can still unlock the flap manually from inside the boot.
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.
Main article: Wipers
The wipers fitted to your car are a classic design, where a simple motor spins around two arms which rotate the wipers back and forth. Operated by their own stalk on the steering column, you have the choice of three speeds; Intermittent, Regular or Fast. Or Off, I suppose. So a choice of four.
Touring models were also fitted with a rear wash/wipe system, which is very useful... when it works. The system is controlled by two switches, offering a wash or a timed wipe setting. Cleaning fluid is sprayed from a nozzle mounted to the wiper arm, and will only operate when the wiper is moving; therefore, pressing the wash button should make the wiper sweep three times.
Because of the complicated plumbing around the Tailgate, leaks in the rear wash/wipe system are very common.
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.
Main article: Cruise Control
A number of components of the E30 were fitted to make the cars more comfortable in colder climes.
The most obvious of these are the Heated Seats. This optional extra involved the installation of heating pats into the base of the front seats, controlled from switches located on the centre tunnel.
Another optional extra was the Heated package. Buyers who purchased this equipment option would be treated to wing mirrors, washer jets and door locks that were all equipped with heating elements, to prevent them icing up. These components were automatic, and would activate either with the ignition on or the unlocking of the car via remote.
If you wish to retrofit any of these components, the main Loom provides all the required plugs in their respective locations.