[Warning Light] Rear heated screen switch light fault.

[bikergraham]

Can anyone throw some light on this.On my MK1 berlingo when i use the rear window heater the light on the switch goes on and off,ah,thats easy i hear you say ,its a loose connection, no it isnt! As you know the light on the switch goes on twice as bright when its on ,so when i just use the headlights it works fine as does all the interior lights,i switch on the heater and it then lights up twice as bright,all good,after a few seconds it goes off,comes on ,goes off,you get the idea,now when i switch the heater back off if the heater light has been illuminated the light goes back to dim ,as was,but if the heater light was in its off cycle and i switch back off,the dim light wont work for 5 or 10 secs,Hmmmm strange.It appears there is a diode and resistor in circuit,does anyone know is this in the switch ?
 Could it be a switch problem ? the heater works whether the light is off or on but my concern is that if it fails completely i wont know if the heater is on or off.