Additional stop lamp control unit
Circuit drawing

The resistance voltage of the electrolytic capacitors that are not designated is a 10V.
The rating electric power of the resistors that are not designated is 1/8W.
Point of contact current capacity of the relay RL3 uses the one that is 3 Amperes over.
( When 2 electric bulb of 12W are used the current of 2 Amperes flows. )