Central locking woes

[NigelCL]

Hello everyone, firstly thank you for adding me to your club. As a new member, and new owner of a 2000 CL500, I was hoping my first post would be a more pleasant one.
I have a problem with my central locking (I think). Every time I operate one the buttons on either of the keys, the 20A fuse for the PSE pump blows. This didn’t happen when I looked at the car, but typically started the minute I got it home. I replaced the fuse, and all the other functions that are operated by the PSE pump work fine, rear headrests, lumbar support, soft close doors and boot without blowing the fuse.
I believe the car had been left stood for a couple of years before I bought it, and have since read that this can cause electrical issues.
My question is, has anyone else had this issue? I would really appreciate a little advice before pulling the car apart in a desperate attempt to find the problem. Is there a logical order of where to start looking, and inspect/repair any potentially failed parts? Thank you in advance, Nigel.

 

[steveskeggy]

If this is all that went wrong electrically after a couple of years stood, then lucky you!
Probably the best thing is If you can get it on a STAR diagnostics, that may well tell you where the problem lies without getting your hands dirty.

If not, then obviously the first thing to do is crack open the drivers door, and disconnect the electrics to the locking mechanism to see if that stops it.
Why drivers door? Well because unless you had a passenger driving it back from the dealers, this is the only door that had been used before the fail.
Even if it does not fix it, it still could be in the loom, the bit between the door and the bulkhead where the loom bends is the usual suspect.
Its a bit of a faff, but if that doesnt work, then you would have to check the other doors individually.
Dont forget though, the petrol filler cap lock and the boot lock are also suspect.
This could give you a bit of a guide, but its no good after 4 minutes.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

You only need go as far as taking the panel off, and the seat adjust panel, then you can trace the leads back from the lock to that panel, pull that plug/s kills the power to that lock.
If you have a later model, the handle does not split down to reveal a screw (44 seconds> into the clip), that screw is now under the seat control panel, and if you try to lever off the handle trim, you will break it (Dont ask me how I know).
If the doors, the boot, and the fuel cap lock test OK, then it could be alarm related, which I dont know about.
Obviously I have only done this on my S-Class, but we are not talking a great deal of difference.

 

[NigelCL]

Thank you Steveskeggy, it’s certainly a good place to start.
I’ve bought this car as a project, I knew it had problems, knew it had been stood, but was mechanically sound and had an mot. Being 20 years old it qualifies as classic, and comparatively low tax compared to newer models.
However, this is my first full day of ownership, and I’m beginning to understand to scale of task. It’s always been a dream to own this car, so figured it was worth spending some time trying to keep it roadworthy, repairing and restoring where necessary along the way.
After a good look at the wiring loom between the drivers door and the car body, it’s obvious that someone has previously attempted some sort of repair in the past. So I think this, and the door locking mechanism seem to be the place to begin. I’m thinking it’s more electrical related as my fuse blows instantly if I touch any button on the keys. I know that the central locking was working last week when it did go for an m-star diagnosis. This wasn’t a problem at the time so didn’t show up on the report.
When I collected the car, the boot was opened too before driving away. So I think that should be the second area to look at.
Two things I’ve noticed that I’m not sure are a factor or not. The battery in the boot is fitted with an isolating switch, presumably fitted to prevent it from draining while parked. And also, the boot release button in the drivers door has a red light on it which remains lit while the ignition is on or the engine is running. Is this normal? I can lock/unlock the door and open the boot with the blade key for now. And the fuel filler cap remains unlocked.