In most vehicles, the parking lights and headlights are typically connected to separate electrical circuits. The parking lights are usually controlled by a switch on the dashboard, while the headlights are usually activated by a separate switch or lever. However, in your 1966 International, the parking light circuit is wired in such a way that it is interrupted when the headlights are turned on.
When the parking light switch is turned on, power flows from the battery to the switch and then to the parking lights. The parking lights are grounded, completing the circuit and allowing them to light up. However, when the headlight switch is turned on, power is diverted from the parking light circuit to the headlight circuit. This interruption in the circuit causes the parking lights to turn off.
This design feature was likely implemented for a few reasons:
1. Conserving Battery Power: By turning off the parking lights when the headlights are on, the electrical load on the vehicle's battery is reduced, helping to conserve power.
2. Avoiding Electrical Overloads: Having both the parking lights and headlights on simultaneously can draw a lot of power from the battery and electrical system, potentially leading to overloads or other electrical issues.
3. Safety Precaution: In some older vehicles, the parking lights and headlights were fused together on the same circuit. Turning on both the parking lights and headlights would draw more current, increasing the risk of overloading and blowing the fuse, leaving you without any working lights.
Therefore, in your 1966 International, the parking lights go off when you turn on the headlights due to the design of the electrical circuit, which is intended to avoid electrical overloads, conserve battery power, and maintain safety by preventing potential fuse failures.
