Check the fuse first, if it's not blown then disconnect it and do some testing at the connector. If the values are correct then its the plug-in that needs replacing. If they are incorrect figure out which wire is bad and trace it back to the faulty area. If might have got pinched and cut somewhere.
The connector could have even just simply corroded. Post all the information you know, if this is all you know you honestly should have looked into it more imo. Also I think this would suit the General MKIII Discussion section. If you're having trouble figuring what threads go where....read the description of them. Good luck.