I have a 1970 xr7. When I turn on headlights the turn signal indicators light up and turn signals stop working.
Something is mis-wired big time. There is no connection between the turn signals and the headlights. Try unplugging the connector at the steering column to see if that has any effect on the issue.
My guess is the turn signal switch. Do you have a tilt wheel?
1970’s have very strange wiring on the side marker lights: no grounds. The turn signal lines are compared to the running light signal. Since your turn signals are coming on, there’s some sort of a ground or feedback issue, typically resolved by a new turn signal switch. This model year is a real bitch to trouble-shoot without grounds.
A test to see if this might be a problem, remove all side marker lamp bulbs and test again. If dash turn signals light up, the problem is elsewhere. If not, add one bulb at a time and see if you can isolate the problem to one of the four side marker lamps.
Also check in the trunk to see if somebody cut out the black box for the sequentials. It would be on the drivers side in the drop off furthest to the left side.
P.S. I have 3, 70 Cougars.
I replaced the LEDs in the front Valance with regular bulbs and the problem went away. I guess the new flasher and sequencer just do the rear lights they are still LEDs but are working fine. Only problem I have now is the left brake light does not come on.
Thank you for your suggestions. I really appreciate it. I have been learning a lot.
The system should work well with LEDs in all positions. Watch the WCCC video about LED light install in my 71 vert. The side markers are integrated in the turn signal system for 70 and 71 only. When you turn on the turn signal without lights on the side markers, front and inboard rear light come on and then they sequence, the side markers get the ground thru the front light bulb filament thus using the socket as a ground. The sockets have a ground wire that grounds on the core support right behind the headlights. When the headlights are on the side markers are on, when you turn on the turn signal the marker lights go out by losing the ground thru the bulb and then flash with the turn filament. Confusing right? If you put the incandescent bulbs in and the lights work I would think you have a “dirty” ground. The incandescent will pull more amperage thus providing a stronger current pushing thru the dirty ground. Clean your bulb sockets good and the core support grounds and put the LEDs back in and see it that doesn’t fix it. Note the front left bulb controls left side markers and right front right side markers. Pulling the side marker bulbs will not affect the turn system.