Driver's door C404 plug

[Ajay325]

Hi guys,

The driver's side [C404] plug on my sport is suffering from corrosion and I'm hoping to re-wire a new plug in, as cleaning hasn't worked.

Can these plugs (both male and female ends) be bought from BMW? If so, how do they come - plugs alone, or plugs + wiring loom.

If anyone has done this in the past, your advice on how hard the job is would be great!

Many thanks
Ajay

[PG325]

I replaced the drivers side with a good second hand one after stumbling across this mess, it didn't take too long, perhaps a couple of hours to soldier in a replacment and swap the door loom.

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[Brianmoooore]

Individual pins and buckets can be bought from BMW, ready for soldering/crimping to the wires, but before you replace anything, you need to understand a bit of what's going on to cause the problem.
First of all, no corrosion takes place if water doesn't get in. The main reason for water getting in is that someone at some time has tried to refit the rubber boot to a plug that was already in the socket. The rubber boot must be fitted to the plug while it is disconnected, and then plugged into the socket with the boot fully in place.
Next, water alone doesn't cause significant corrosion. It requires electricity as well, and most of the pins in the plug do not carry anything for most of the time, although corrosion will spread to these pins from any nearby pins that are corroded.
There are two pins which are live all of the time, so these two are the main problem. One of the pins is fed from fuse 27, goes into the door, and then loops back to the other pin, and out to the central locking ECU. By cutting these two wires at the A pillar socket (work through the hole for the RH speaker in the footwell) and soldering them together, these permanently live pins are eliminated, greatly alleviating the corrosion problem.
This is a common cure for non working central locking, and is commonly known as the "red/black wire modification" .
The only other pins in the plug and socket that carry power for any significant length of time are a couple associated with the electric mirrors, but these are only live with the ignition on, so cause much less trouble.

[Ajay325]

Thanks Brian.

Indeed, my electric mirrors have stopped working this week - hence why I felt to change the plugs completely! Hoping it will also fix the central locking issue I mentioned in a previous post...

[Brianmoooore]

Like I say, the central locking wire is the cause of the 404's problems. Don't replace these pins under any circumstances. Just cut the wires and join them behind the speaker.

[Ajay325]

Thanks Brian, do you think a good plan of action would be:

a) Red/black wire modification
b) Replace any individual pins which have corroded/broken with new BMW pins

I'm not entirely sure what is causing my central locking problem. If you recall my previous post - it was essentially a jammed passenger side door pin which was refusing to open with the central locking or manually. I removed the actuator and it was fine (not jammed).

I've now taken the actuator off for the meantime -> the lock functions nice and smoothly, but is obviously now not part of the central locking system.

Do you think the red/black wire modification will resolve this? I couldn't get my head around why a corroded power lead would cause these problems with the passenger lock!

[Brianmoooore]

Thanks Brian, do you think a good plan of action would be:

a) Red/black wire modification
b) Replace any individual pins which have corroded/broken with new BMW pins

Sounds about right, but things have to be really grim in there to need to replace pins. A brass wire brush and a fibreglass contact cleaning pencil can work wonders, along with a good dose of silicon grease over everything when it's all plugged back together.

I'm not entirely sure what is causing my central locking problem. If you recall my previous post - it was essentially a jammed passenger side door pin which was refusing to open with the central locking or manually. I removed the actuator and it was fine (not jammed).

I've now taken the actuator off for the meantime -> the lock functions nice and smoothly, but is obviously now not part of the central locking system.

Do you think the red/black wire modification will resolve this? I couldn't get my head around why a corroded power lead would cause these problems with the passenger lock!

Central locking that needs the red/black wire mod. either is absolutely dead, or just gives a buzz from the locking ECU when operated, but if the pins on the red/black wire had decided to quit while the car was deadlocked, the passenger door would be unable to be opened, since the only way of releasing the deadlock is electrical.

[Ajay325]

Fantastic, thanks for your advice!

Will crack on with this and report back in due course.

Ajay

[Grrrmachine]

Brian, do you know know which pin and socket on the RealOEM diagrams are the ones used in the C404?