Headlights On Warning Buzzer - How to trouble shoot?

[PurpleBeeper]

70 road runner rally dash A01 light group (if that matters).
1. I got my “key in” warning buzzer working, but the buzzer doesn’t go off if I leave my headlights on.
2. I installed a home-made headlight buzzer diode
How do I diagnose & repair the headlights on warning buzzer? I have the factory service manual, but this is a very complicated circuit. Any advice to share? THANK YOU!

 

[pnora]

Only 3 wires pretty simple.

 

[PurpleBeeper]

Only 3 wires pretty simple.

Can you explain please? I’m seeing 6-8 wires in the circuit between the dash wiring diagram and the accessory wiring diagram

 

[pnora]

Doesn't the key in buzzer only have 3 pins?

 

[PurpleBeeper]

Doesn't the key in buzzer only have 3 pins?

Yes, the buzzer has 3 pins and the buzzer works with the key. The problem I have is that the buzzer doesn’t work when I leave the headlights on. It looks like the headlights & key use the same buzzer. The headlight wiring is much more complex with a diode & more wires