where do the lights ground to i have checked all sockets have found blacl coloration on thim but fillimants are still attached

the schematics on this car are very complicated the ground is actually going through the switch however usually on this car there is a 20 wire connector on the frame under the battery that gets corrosion on it from a leaking battery or road salt most times i would just cut the connector out and hard wire the circuit together and that usually fixes the issue of no or dim lights

as i said i have head lights running lights i was told to check my sockets which i did starting from the passenger side i did find a turn signal running light buld slightly blackened but filliment was still connected so i replace it anyways and still no turn signal brake lights or four ways now what