Buzzers - Speed Warning, Key Reminder - Theory of Operation?

[Big Kev-O]

The camaro buzzer has 3 terminals but only two were used to activate the buzzer. The third terminal was used to keep factory plug orientated so that the wires didnt get reversed. The camaro buzzer has 12+ running to it and is activated when the circuit is grounded by the speedometer when it hits the limit. GM cars that were originally equipped with speed warning buzzers had a speedometer with a special terminal to ground the circuit. You need a way to complete a 12v circuit at a given speed. Does your speedometer have the connector/terminal that provides a ground? If it does you can use the Camaro buzzer or a typical 12v relay in conjunction with any 12v audible device for a speed buzzer.

[davepl]

Originally Posted by Big Kev-O

The camaro buzzer has 3 terminals but only two were used to activate the buzzer. The third terminal was used to keep factory plug orientated so that the wires didnt get reversed. The camaro buzzer has 12+ running to it and is activated when the circuit is grounded by the speedometer when it hits the limit. GM cars that were originally equipped with speed warning buzzers had a speedometer with a special terminal to ground the circuit. You need a way to complete a 12v circuit at a given speed. Does your speedometer have the connector/terminal that provides a ground? If it does you can use the Camaro buzzer or a typical 12v relay in conjunction with any 12v audible device for a speed buzzer.

It's got all that of course and that all works. The problem is only the buzzer part of the circuit. There is no normally-closed contact that I can find. So you have to power the buzzer with 12V and then have the trigger from the speedometer ground out that 12V so the coil collapses and the relay 'clicks', and it repeats.

That grounding melted the little test wires, but before I just assume the factory harness can handle that load and I burn down my truck, I need to understand it better.

Maybe a resistor in line? If some electrical genius wants to draw a diagram with a better way, I'd love to see it. I'm trying to find a schematic in another thread, no luck yet.