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The main Loom contains all the wiring for your E30. It forms the core of the Electrical system.



From the front to the rear Lights and everything in between, the wiring inside your E30 is a combined unit that accommodates all the primary functions of the vehicle. This bundle of cables is known as the Loom, and its hub is the fuse box, mounted on the inner wing inside the engine bay.

The Loom is a standard design across all E30 models, with minor differences between years. Unsurprisingly for BMW, its design means that every element is fed with its own custom-made socket to make connection and disconnection of each component simple, and a standardised wire colour scheme means that cables can easily be identified by their colours and location.

Secondary looms for removable or optional components, from the engine to the radio, make use of sub-looms that connect to the main loom at special plugs. These plugs are referred to by letter and number, and start with the main engine plug, the C101.


Fuse Box

Main article: Fuse Box

The Fuse box is the beginning and end for every key wire in your car. Mounted inside the engine bay against the bulkhead, it is a single-body unit with up space for 30 fuses and 10 relays, 8 of which are removable.


Main article: Relays

To help switch components on and off, a number of relays are fitted within the loom. We've documented their locations, so that you can locate the source of that irritating clicking sound.

Accessory Socket

Located under the glovebox on RHD vehicles, the Accessory Socket is a multiplug port that allows quick fitting of optional extras, without having to splice into the main loom. It is referred to on wiring diagrams as C302.

Terminal Circuit Terminal Circuit Image
A Not used N Not used Accessory.jpg
B Not used O Not used
C Not used P Not used
D Central Locking Q Power Windows
E Not used R Cruise Control
F Not used S Cruise Control
G Not used T Not used
H Board Computer U Heated Seats
I Not used V Radio
W Radio
K Not used X Radio
L Not used Y Radio, Ground
M Not used Z Antenna


The whole point of the loom is to connect each electric component in the vehicle, and therefore the whole mass of wires is populated with multipin, multicolour and multi-purpose plugs. While it would be impossible to document every single plug in the vehicle, we can list some of the most important ones here.

If you have found a plug and aren't sure what it's for, check the wiring diagrams.


Main article: C101

The biggest terminal point of the car loom is the C101 plug. This multipin connector sits in the engine bay (usually on the bulkhead), and allows the different engine looms to connect to the standard vehicle loom. This means that you can disconnect, remove and replace an engine without disturbing the main wiring for the vehicle.

Because all the engine wiring runs through this plug, it's a great place to start looking for wiring problems when troubleshooting. A full pin-out of the C101 plug is contained in the main article.

WARNING: There is one difference in the C101 design between many E30s, and that is Pin 20. On early vehicles, Pin 20 is a brown earth wire, while for some later vehicles Pin 20 is a live, unfused red/yellow wire for the ABS system. If you are changing your engine, CHECK PIN 20 ON BOTH SIDES OF THE C101 PLUG before connecting the battery.

If you have a brown wire connected, cut it away from the pin, and make sure the free end can't come into contact with anything. If it is red/yellow, then leave it alone. Of course, if the body side of your C101 has a red/yellow wire on pin 20, and your new engine loom has nothing connected to this pin, you need to add a wire, capable of carrying about 15A, from either of the terminals marked '87' on the DME relay socket to pin 20 of the the C101 plug, otherwise your ABS braking system won't work.


Main article: C191

The C191 plug sits in the engine bay, underneath the intake manifold. It is the main plug for the fuel injectors, but also carries coolant temperature information to the ECU and temperature gauge. It is a known problem area for E30s, and can be the source of a number of engine problems.

Door Loom

Main article: C40x

Referred to by BMW as connections C404 and C405, the door loom plugs are fitted into the A-pillar of the shell and allow the doors to be disconnected for removal. Because of their location and exposure to the elements, the various pins of these connectors can corrode and break over time, leading to a general failure of components such as the electric windows, mirrors and especially the central locking.

A full pin-out of the door loom plugs is contained in the main article.

Wiring Diagrams

Main article: Wiring Diagrams

BMW didn't try to document the loom all in one go, and we won't either. But the Wiki does contain diagrams collected from a number of resources, broken down into sections to help you troubleshoot your electrical problems. Check out the Wiring Diagrams for a complete list.