S124 Alarm/Immobiliser problem

[swannymere]

Just replaced the battery on my S124 E300d and when i open the door the indicator's blink on/off for about 30 seconds and the starter motor doesn't turn over when i turn the key in the ignition.
Is it most likely that the the alarm/immobiliser has kicked in? I don't have any fobs or idea of location to disable it, so is my best option having it removed and a new fitted? A company local to me advertises a mobile service to cut out the old one for £75 or £150 to remove the old one and fit a new immobiliser.
What's the best course of action?

 

[SilverSaloon]

if it is like mine then there will be a key under the dash somewhere where you can bridge the wires.

 

[Dec]

When you reconnected the battery the alarm rearmed itself as the cars electrics were being “tampered” with by you.

The alarm finds a door/bonnet or tailgate open so it is triggered… had you then unlocked the car the alarm may have disarmed and you should have been able to start the car. After 30 seconds the alarm reset itself so that was normal.

As the siren didn’t sound when the alarm was triggered then it might just be faulty, replacing the siren with a known good one from a scrap yard MIGHT? solve the fault.

Try locking yourself in the car, stay still for 60 seconds then open a door, the alarm should be triggered again… except for the siren… unlocking the car should then disarm the immobiliser and disarm the alarm, allowing you to start the engine.

How many wires are going into the siren?

Dec