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The controller ground the blower motor and the blower motor supplies power to the blower motor. The blower motor relay is energized by the ignition switch. So you need to check to see if the blower motor is missing power or ground, probably power. If its missing power replace the relay to see if problem goes away if not check the 10 amp relay fuse and the 30 amp blower fuse. Then depending if they are good are not you will need to see if the relay clicks. If relay doesnt click then you will need to see if red wire going to relay has power if not replace wire between relay and ignition switch. If it has power then check black wire for good ground if not then run a new ground to it. If relay does click then you need to see if blue wire has good power if not replace blue wire between relay and 30 amp fuse. If it does have power replace red/green wire between relay and blower motor. Here is a wire diagram, let me know if you have questions. Thanks
2003 Jetta left rear window blue plastic part of the