C40x

The C404 and C405 plugs are the door connectors on the vehicle Loom. They allow the door wiring to be disconnected from the rest of the vehicle, so that the doors can be removed easily.

The plugs on the A-pillar. The C404 connector is for the right door and the C405 connector is for the left door. The male portion of each connector (the pins) is on the cabin side of the vehicle, and the female portion of each connector (sockets) is on the door side of the vehicle.

Because the E30 was primarily designed for the domestic German and export US-markets, the wiring is designed around a driver seated on the left, and therefore the C405 plug carries more info than the C404. Where possible, C404 equivalents have been listed in the table.

Removal of the male portion of the connector is straight forward. Pull back the rubber boot to expose where the female portion of the connector connects to the male portion of the connector. Pull the female portion connector away from the male, then use a flat-head screw drive to release the three clips that hold the male portion of the connector to the cabin. Remove the speaker cover in the footwell and the speaker itself, then fish around inside the A-pillar to get access to the C40x plug.

The wiring that passes through the C404 and C405 forms a key part of the Electrical system.

C404 Pin	Colour	Function	To	Image
1	Blue/Black	Electric Mirror	Mirror Motor
2	Blue/White	Electric Mirror	Mirror Motor
3	White/Black	Electric Mirror	Clutch Solenoid
4	Brown	Electric Window switch	Ground G200
5
6
7
8
9	Blue	Central Locking	Door Locking Motor - lock
10	White	Central Locking	Door Locking Motor - unlock
11	Yellow/Blue	Central Locking	Microswitch - Lock
12	Green/Blue	Central Locking	Microswitch - Unlock
13	Violet/Blue	Electric Windows
14	Black/Blue	Electric Windows
15
16
17
18
19	Black	Central Locking
20	Grey/Green	Speakers	Tweeter
21	Green/Yellow	Speakers	Tweeter

C405 Pin	Colour	Function	To	Image
1	Green/Black	Electric Mirror	Fuse 19
2	Brown	Electric Window switch	Ground G200
3	Red/Black	Central Locking	Fuse 27
4
5	Blue/Black	Electric Mirror	Mirror Motor
6	Blue/White	Electric Mirror	Mirror Motor
7	White/Black	Electric Mirror	Clutch Solenoid
8	Brown	Ground
9	Blue	Central Locking	Door Locking Motor - lock
10	White	Central Locking	Door Locking Motor - unlock
11	Yellow/Blue	Central Locking	Microswitch - Lock
12	Green/Blue	Central Locking	Microswitch - Unlock
13	Violet	Electric Windows
14	Black	Electric Windows
15	Red/Black	Central Locking	Central Locking module
16	Brown/Blue	Central Locking
17	Red/Brown	Central Locking	Inhibitor Switch
18	Green/White	Interior Light	Interior Light delay timer
19	Brown/Green	Interior Light	Door Handle switch
20	Grey/Green	Speakers	Tweeter
21	Green/Yellow	Speakers	Tweeter

Parts

If your pins are corroded and your plugs brittle, it's worth replacing the sockets and pins to ensure your locks and mirrors work as they should.

You can buy complete looms from BMW; however, for a fraction of the price and a few hours with some crimping pliers (no soldering required), you can strip and rewire your own plugs by ordering the following parts:

Item	Part Number	Quantity
C40x Female socket holder	61131375688	2
C40x Male plug	61131380587	2
C40x pin holder	61131375690	2
Pin	61131371605	33
Socket	61131371607	33

On the male side, the pin holder carries the main pins (5-22), which then clips into the male plug. The male plug also holds 4 pins of its own - pins 1-4.

You may find that the significant chunk of this cost is the individual pins and sockets. In case of price changes from BMW, it may be more economical to source these pins from a third party. In this case, you're looking for 1.6mm pins and sockets such as these and these.