Advice pleas.

Son's VRS has intermittent alarm fault - going off randomly for no reason.

Searching indicates it to be a common fault and possible causes are:

1) draft from air vents

2) volumetric sensor faulty

3) boot light switch fault usually due to corosion from disconnected rear window wash

4) bonnet "open" switch

Have eliminated 1 (alarm still goes off randomly even in a draft free place) & 3 - (rear wash working fine - no water dripping from hatch door)

But having problems with 4) bonnet switch and am trying to understand whats going on.

Does closing the bonnet make the circuit open or closed ?

I can turn alarm ON with the bonnet still open - this is wrong isnt it ? shouldnt I get a signal as if a door was open ?

If I disconnect the wiring from the bonnet switch, I can turn the alarm ON with the contacts in the wire terminal open or bridged with a bit of copper wire and the alarm remain silent.

But the alarm goes off if I either bridge the open circuit or if it is already bridged I open the circuit then rebridge it again.

If I reconnect the wire to the switch and turn the alarm ON , pressing the contact on the micro switch (making the switch click) does NOT cause the alarm to activate .

Therefore I conclude the micro switch is at fault and needs replacing.

Does you agree ?

Also, if you lock the car by turning the key in the driver door - does this deactivate the door and bonnet switches ? - I know it deactivates the internal volumetric sensor.

All advice gratefully received.

As far as I know locking the car by the door lock activates the alarm in the same manner as the remote. If you lock it twice it deactivates the internal sensors the same as the remove and the deadlocks wont set.

If the bonnet switch is faulty the int wipers wont work. Usually disconnecting it deactivates it.

The alarm has a settle time after arming while is scans sensors and their state. Hence if the bonnet switch is faulty the alarm will set and disregard than sensor. However, if the sensor then changes state while the alarm is set, an alarm is triggered. IIRC the swtich is open when bonnet open.

As far as I know locking the car by the door lock activates the alarm in the same manner as the remote. If you lock it twice it deactivates the internal sensors the same as the remove and the deadlocks wont set.

If the bonnet switch is faulty the int wipers wont work. Usually disconnecting it deactivates it.

Well thats what i thought would happen but after disconnecting the bonnet switch the int wipers still work fine !

Really confused now !

Have left the bonnet switch disconnected and the alarm appears to activate OK and not go off randomly. Will look to replace the micro switch in due course. Can you buy just the switch or does it come with the whole bonnet latch mechanism ?

any final outcome on this jules?