W124 Coupe central locking issue

[paulcarr50]

Hello,
I've a 1996 W124 coupe.
It's fitted with an aftermarket alarm which I use to lock and unlock the car.
No problems with this since I got the car and 8 years ago.

Last summer; the car battery went flat and I replaced it with one from a w204.

Since installing this battery; I now have a problem with the car randomly locking itself.

Usually this happens when I shut the drivers door but other times I can close the drivers door and car remains unlocked.... Then an hour can pass and out of the blue.... The car locks itself.

This happens even when I'm driving the car.

Does anyone have any tips / suggestions to resolve this fault?

I took the drivers doorcard of this evening to see if wires were frayed or anything else was amiss but no smoking gun.

Any help gladly accepted.

Thanks

 

[alabbasi]

Your car has pneumatic central locking , operated by a vacuum pump. The alarm central locking module is probably located near the vacuum pump. Not sure where that would be in a W124 but in a w126, it's bead the spare where (which would be my guess for the w124). On the W210, the vacuum pump is under the back seat

 

[paulcarr50]

Thanks for the reply alabbasi...
The central locking pump I located under the rear seat drivers side...
It's fine as far as I can tell.

The aftermarket alarm is fitted under the steering wheel area....
All connections are grand...

When the car randomly locks.... The alarm does not arm.... I'm taking this as meaning the alarm is not there issue.
I also contacted the alarm provider... Very helpful fella and he is of the opinion that the alarm is not the cause.

The search continues!!!