My son and I are rewiring his '69 Bronco with an Ez-Wire street rod harness. All of the wires are marked full length as to what they are for. We wanted to check to make sure everything worked correctly after we installed the instrument cluster and check all the indicator lights. When I turned on the headlights to check the high beam indicator, the indicator was lit but he said the headlights were on low beam. We checked and double checked everything and all the wiring looked right. We even swapped a couple of wires to make sure. We checked it further and found out that when the high beam indicator was on the right headlight was on bright and the left was on low beam. Now we were really puzzled because they were wired correctly. When I pushed the dimmer switch to change the lights to low beam, the right one would be low and the left one would go to high beam, every time I pushed the dimmer switch they would be opposite one another. I realized that we didn't have the ground connected on the left headlight, so when I connected the ground it worked correctly. I know grounds are very important, but I didn't realize that an ungrounded or improperly grounded headlight would still work, but swap beams. Moral of the story, Have proper grounds!
Mark

 

Grounds or lack of definitely do weird stuff. Troubleshooting them makes for a great learning experience.

The problems that give us the most trouble make us REALLY think. I always learn the most from them.

Glad you got it figured out!

 

A similar but not quite situation with my sons car. Said the headlights were dim, not as bright as usual. We checked the battery and alternator, both were good. So next were the grounds. All scrody and stuff. He learned how to clean them up while I stood and had a frosty root beer. Good as new now.