66 dart electrical problems

Recently I had the no headlight experience in a field car I resurrected. Lights had been working fine and simply quit. It turned out to be the Hi/Low dimmer switch. All headlight power (but not park light function) from the dash switch is routed to it first before it goes out the bulkhead connector.

The stated fact that the turn switch initiates the horn screams crossed wire. However it could be as simple as the moveable portions of the switch are somehow engaging/moving the copper horn ring on the underside of the steering wheel to ground. I'd consider pulling the wheel, if on, to test this as well as to diagnose the turn switch itself. The copper horn ring behind the steering wheel does wear out typically going to ground and turning on the horn permanently. Or some folks don't realize that during reassembly of their restored sterring wheel that this copper disk needs to be electrically isolated from the steer steering wheel body at reassembly.

Typically if you fix the blinkers the brake lights will work as the are both controlled by the turn switch mechanism. To diagnose the turn switch I'd separate it from the connector to the main harness, power it up with a jumper wire and using your test light activate the switch see if the test light blinks appropriately. Also on brake lights one can't forget the activation switch at the pedal. these can become corroded over time and/or do wear out. I've had good success in fixing these by simply rotating the movable portion back and forth in a clock/counterclock wise fashion to remove built-up corrosion that can prevent it from sending a signal. this is even true of 50 year old NOS pieces that have sat on a shelf. New yes, but time takes it's toll especially if improperly stored.

Hope some of this helps.