Engine immobilised

[Fluffy300]

Hi, I’m new here,

l have just acquired an is 300 saloon for it’s age in quite good condition.Since owning it l have been fixing bits and pieces that needed attention one job was to replace the Battery terminals.Obviously to do this the Battery needed to be removed.  I Completed the job and refitted the Battery and now the engine will not start everything works with the ignition on but the engine will not fire. The only thing I did think was odd the alarm does not operate when the car is locked and the door or boot is opened where as before the Battery job everything was fine this is what has made me think the immobiliser is at fault. Any info would be a big help.

[ColinBarber]

Put key in ignition, turn to on and leave for 6 minutes - the immobiliser and key should synchronise and the immobiliser/security light should go out.