I constructed a manual traffic light. I am using 12v LED light bulbs and a three way switch ON=green light, OFF=red light, so far that was easy. I would now like to add that when I switch to the red light an amber light flashes for about 5 seconds then the red light goes on and stays on. Any suggestions about how to build the circuit and what exact supplies I will need.
TIA

 

at the very least some sort of digital logic (or a complex analogue mechanism). i feel like a micro-controller would do what you want, but you would have to write software for it.

 

I constructed a manual traffic light. I am using 12v LED light bulbs and a three way switch ON=green light, OFF=red light, so far that was easy. I would now like to add that when I switch to the red light an amber light flashes for about 5 seconds then the red light goes on and stays on. Any suggestions about how to build the circuit and what exact supplies I will need.
TIA

You could use a pair of 555 timers or a dual timer 556. One to give a 5 second delay, and the other to flash the yellow for seconds. If you could post a diagram of how you have the switch wired now, I will be happy to help you with the rest.