Motorcycle seat heater element installed, no listed rating. Using 12 volts across leads I measured 2.76 Amps current draw. How can I simply wire it to give approximately half-power and full power for two levels of heating?

 

Motorcycle seat heater element installed, no listed rating. Using 12 volts across leads I measured 2.76 Amps current draw. How can I simply wire it to give approximately half-power and full power for two levels of heating?

You could place a ~10-15W, 12V lightbulb in series with the heater and place a switch across the bulb, so you can short across it. When the light is on, the heater will get only about half the voltage and current that it does at full power. That would take it to 1/4 power, so that's why you may have to experiment with the bulb wattage to get the heating result you want. Of course you could use a power resistor instead of a lightbulb. It needs to be ~3Ω and rated to at least 10W. Like the lightbulb, it will get hot.

You COULD get yourself a PWM controller and that would give you smooth control from end-to-end. The controller needs to be rated for your usage - I'd look for a 5A rating just to get some headroom. These are pretty darn efficient, so I don't think it will get terribly hot. Check on eBay. I don't think it'll cost too much.

You could build your own if you're in the mood for a project. It may not be any cheaper than one off eBay.
https://www.electro-tech-online.com/articles/simple-pwm-circuit-for-lamp-dimming-etc-improves-on-555-pwm-circuits.797/