We found this circuit in a Motorola manual. The circuit has the capacitor charging at 15 to 30 V, then discharging through the coil and generating a voltage that reaches 500 V for the spark plugs.
This circuit, from a 1973 publication, locks the relay when the light that falls on the LDR is cut...
We found this circuit in a Popular Electronics of the 90s. Its purpose is to detect when it locks...
This circuit is from 1987 when there were only analog TVs and stereo sound was still a novelty for this...