Here is a weird one. I replace all the outside light, except the headlights. With LED. I read there is some weird thing where ford uses one of the filament bulbs for ground return, which is why I have left the headlights for now. Here is my issue... With the headlights off, all my blinkers work fine. When I turn on the parking lights or the headlights. The blinkers stop working and the front side marker lights go out. The ones under the bumper keep working, its a 70. I had bookmarked some LED light grounding adapter, but I didnt think I needed it with traditional headlights still in, but now I cant find it.
Found my book mark http://mmb.maverick.to/threads/led-head-light-conversion-problem.127409/#post-1174292
