To give a better and less cheeky answer:
If you look at the section of the wikipedia entry called
Astable Mode , that's describing the kind of circuit you want to build around a 555 timer to get it to flash a small LED, for example. In the diagram there labelled "Standard 555 Astable Circuit", you would put an LED and a resistor of appropriate value (to get the LED's voltage correct) between the line marked OUT and ground, and you've got a flashing LED. Adjusting the values of R1, R2, and C1 in that circuit according to the formulas on that page allows you to change the blinking frequency, and specifically changing R1 and R2 relative to each other allow you to change the duty cycle (like, whether you want the blink to be on for 200ms and off for 800ms, or on for 500 and off for 500, etc).
Once you figure out how to blink an LED at the desired frequency and duty cycle with a 555 timer hooked up to a little 5V power supply, the next step is how to integrate this with the F1 rear light ideas.
First, to run off of unclean 12V car power, you'd want a voltage regulator to deliver power to your little circuit. A
7805 will provide your circuit with a stable 5V power supply, and can be driven by 7-25V DC on the input side, which is perfect for car input.
Then there's the output to consider. The OUT line on that 555 circuit (pin 3 of the 555 timer) can't source enough current to actually drive the rear lamp directly. It would just fry the chip if you tried. So you want to find a small transistor (or really, a small relay might be even better) that the 555 can drive, which in turn delivers the full current 12V to the rear light.
The next step is to sort out wiring up the heated seat switch's two on positions and the reverse gear sensor of the car to get the desired effect (normally off in the rear position, normally on when in the forward position, and controlled by the 555 timer output when reverse is engaged in either switch position), which isn't too hard, but I haven't thought it through yet either
