Ah the GM Buzzer Box that a lot of people used to pull out and throw away!
Pin 1 - Accessory Power +12 V when key is in run position or accessory position
Pin 2 - Seat Belt Lamp (positive output)
Pin 3 - Ground
Pin 4 - Grounded when drivers seat belt is plugged in
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Pin 6 - Grounded when key is in ignition cylinder AND door is open. goes to key minder switch in column, other side of that switch goes to door pin switch.
Pin 7 - Battery + 12 V always
Pin 8 - Not used on my 79
Pin 9 - Not used on my 79
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The buzzer box internal schematic is drawn wrong by GM I believe. Pins 3 and 4 are reversed. I have corrected them in the 2nd diagram.
Function 1:
If you open the door AND leave the key in the ignition, Pin 6 is grounded, which completes the circuit thru the buzzer to battery positive.
Function 2:
When you turn the key on, power flows from Pin 1 thru the normally closed contacts of the relay out to Pin 2 which turns on the seat belt light and forward biases NPN transistor Q1 which turns on the buzzer. When you plug in the seat belt, Pin 4 is grounded thru the switch in buckle and the relay coil is energised thereby turning off the buzzer and light.
I'll have a look and see if I can figure out what your brown and orange wires r.
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