I'd like to design a simple device that uses a microcontroller (in my case a TI Tiva C Series Launchpad) and a relay to drive a load, then monitor whether the load is actually drawing any current. The load will draw about 5-10 A at 12 VDC. What is a good method to determining if the load is actually drawing any current so I can use that as feedback into my microcontroller for other functions? What electronic components would be used?
I'm essentially trying to duplicate how my car knows if I have a failed headlight. If I flip the switch to the headlights, a signal to an ECU that then commands a relay to close. If the relay closes, but the lights don't come on, I get an indication on my dashboard info panel (not a dummy light, but a text readout; in other words, the indication comes via the ECU). The only wires going to my headlights are two power wires (one each for high and low beams) and a common return/ground.