So I won a speedo from an RS, I have a left hand drive AUM. I was thinking of plugging it in and see what happens. What is the worst it could happen?

If its from a left hand drive, won't it read in km/h?

Speedo forms part of the immobiliser also iirc....!

It will probably throw up a fault code 'engine start blocked by immo' which will need to be cleared before you can start the engine.

thats all? Will it do this every time? Or just once?

I ve read about EEPROM and VAG Pin reader or something like that, if anyone wants to point me to the right direction please feel free

Sorry I thought you meant to jet test it worked, if you meant that you wanted to swap out the cluster then you will need to match the immo to the ecu, you will need the pin number for it, the ecu is only capable of being match to one cluster at a time.

or you can get the immobiliser mapped out

anyone knows the type of smd led neeed for the needles? plcc2 but what voltage etc? Any good guides around?