There's a good chance your coolant fan thermo-switch is failing, causing the fan to stay on. Here is what it looks like - http://www.evwparts.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=1H0959481B&Category_Code=NewBeetleCooling
A simple test would involve disconnecting the fan switch while the fan is on. If the fan then stops the switch has failed. If the fan continues to run remove the relay , if the fan then stops the relay has failed.
Various inputs/outputs at the relay should be confirmed to be 100% certain something strange isn't going on.
Above all be careful of the fan itself , if it's running obviously but if it's not it could start during repair or at any time!