Hello, swice
The headlights on warning buzzer is part of the "Convenience Group" option for all 71-73 Mustangs and Cougars. It included trunk, glove compartment, map, under hood, under instrument panel (standard on verts), and park brake warning lamps. It also included the lights on warning buzzer, automatic seat back release (not available before 1/71), and glove box lock. A lot of nice components in that option.
The buzzer is a multi-use item for the key, headlights, and seat belt warning. It is located on a panel above the glove compartment door. The buzzer went through several replacements so I'll list just the top five part numbers and the corresponding engineering numbers to help you.
DOAZ-13150-D (ID# DOAB-13150-D, G)
DOAZ-13150-E (ID# DOAB-13150-B, E, F)
D2AZ-13150-C (ID# D2AB-13150-A1A, A2A)
*D2AZ-13150-D (ID# D2AB-13150-BA, D3AB-AA)
*D4AZ-13150-B (ID# D3AB-13150-BA, D4AB-AA, A1A, D5AB-AA, D5ZB-AA)
*The last two were the best since they had a radio suppression diode to correct a noise problem.
Just in case you might need one, the headlights on relay is D1AZ-10C838-A (ID# D1AB-10C838-AA)
You can search by Ford part number on E-Bay, or contact Don @ Ohio Mustang Supply, Mike @ Motor City Mustang, or Midlife and see what they have.
