Octavio

Hi everyone, l am from mexico and l have a golf vr6 1992 oem but l have been having a big problem, l hope you can help me the problem is when l down or up the window electrical or l use the headlight the voltage down and the interior light too, l checked the ground and positive wiring and its fine (not resistance) new battery and alternator, its happend with on/off car Any advaice please thanks a lot!