why have a relay fitted with resistor ?

does it stop back feed ?

Depends on where the resistor is and what it's used for. Can you give us a diagram?
Taking a totally uninformed guess, it may be to stop the source of the switching current being pulled to ground..or it could be an open collec....oh. VW, not electronics. Sorry. Diagram please :P

Anyway, you usually use a capacitor to help with damping spikes and smoothing off abrupt terminations of power. Resistors provide balance to the force :vader

Some times they put a multi mega ohm resistor across the relay coil, because it, as coils do, generates a spark when its field collapses. this resistor grounds the spark, while not allowing any significant current flow under normal operating conditions.

Are you sure it's not a diode?

I was taught to use diodes for spike suppresion, though I can't think of any reason you would need to use this on a vw

I tend to use capacitors. They soak up all the surging electrons. That's on the main current, not the switching current. Put a cap across the switching pins and it may be a while before your relay turns off.

It's just occured to me that it could be there to prevent radio interference from the switching contacts.

BajaChris wrote:It's just occured to me that it could be there to prevent radio interference from the switching contacts.

That would be by damping sparks, wouldn't it? If so, makes sense to me.