Alarmed central locking not working

[ck89]

97 ek9 - Clifford 650 concept
When I press the arm/disarm on the alarm fob it arms/disarms the car, but it wont open or close the doors ( it used to but stopped working)
Today I noticed if you turn the ignition off and leave the lights on, when you press the arm/disarm button on the alarm fob, the alarm arms/disarms and locks/opens the doors itself?

Any ideas why this is happening?

 

[type-r-dunk]

It will most likely be the solenoid in the drivers door, pull the panel off and see if its trying to work. Only a couple of pounds and really easy to fit. I might have one here if you want it.
Dunx

 

[ck89]

Why does it only work when the lights are turned on though? Works absolutely perfect while the lights are on, turn the lights off and it doesnt work what so ever?

To me it seems like it needs power to work but is getting none, but if you turn on the lights there is power and it works perfect.

the solenoid seems fine. I dont get how it only works while the lights are on?