My main beam only works on one side. There is a few volts showing but not enough to light it. Can anyone tell me where to chase it back to? Any ideas where it splits or where I test its origin. The drivers side has 12v and is perfect but not the passengers, it only has 3v. Do both sides leave the switch or just one wire that goes somewhere before it splits further down the line. Any thoughts appreciated. 1996 300tdi 90.