I build a brake-light failure detector for a car a long time ago. A reed relay with the wire wrapped round it. I put enough turns on so that it would cut in with both bulbs on, and not with only one bulb. Any good for your application?
I build a brake-light failure detector for a car a long time ago. A reed relay with the wire wrapped round it. I put enough turns on so that it would cut in with both bulbs on, and not with only one bulb. Any good for your application?