This flasher gives 3 to 8 flashes, at reduced intensity, and then goes solid. They do not have the 'strobe' effect in any way or form.
Q1 is a PNP Silicon 'Audio Power Out/Medium Power Switch Transistor', 7A, with a TO-220 case. As long as you have a transistor which is close it will work fine. The SCR is a 100vrm, 0.8A, sensitive gate with a TO-92 case. Diodes D1, D2 and D3 are standard small signal diodes. Power diodes D4 and D5 are the 6A, 50prv types, cathode case. The 60vrm type will work as well. I used for IC1 & IC2 the LM555 type. P1 controls the 'on' and pulse-duration, P2 controls the pulse-timing.
Applying the Brakes: When you first press the brakes, this circuit will turn on your 3rd brake light via the main brake lights. After about a second a series of short pulses occur. The number of pulses can range from approximately 1 to 10, depending on the setting of P1/P2 and when the brake pedal was applied last. After the pulses have been applied the third brake light assumes normal operation. The prototype was set for five flashes which seemed more than enough. Two days later I re-adjusted the trimmer potentiometers for 4 flashes.