i have no driving lights in low beam mode. high beam all 4 headlights work.
naturally i thought dimmer switch/ headlight switch. no dice, changed both out and still have same problem. i have the cadillac tech manual but its vague on this problem. can't be a ground due to all lights working on high. any thoughts?

 

Hey Mav: Not sure if you have the guidematic headlights on the 77 models or not. If you do these guidematic lights have a relay and an amplifier assembly on them.Do you have any type of photo cell dimming feature or twilight sentinel??

 

ya i have twilight and sentinal. i swapped the guidematic relay with my buddies 78 eldorado and it did not fix the problem.i'm assuming sentinal is the high beam /low beam with sensor in grill. that works but the feature for turning lights off automatically does not work(twilight)i'm aware the sensor is in the dash/left side near window. will check that next