Need a simple courtesy light circuit

the IC chip will control the timming, other than that, you can use a timer relay to shut off the signal for the dome light circuit.

the problem is the low resistance of the dome light...

lets assume it is 30 ohms, lets say the light will still be lit until about 6 V (unlikely though).

If we place a capacitor across the dome light we will have an exponential decay when power is removed....

So the equation of the dome light voltage becomes: V(t) = 12e^(-t / tau), where t is time and tau is the time constant (R*C)

if we assume resistance is 30 ohms.... what capacitance would we need for say 30 seconds of light...?

so after 30seconds we need 6 V or higher...

6 = 12e^(-30 / (R * C)).... R = 30 so...

6 = 12e^(-1/C)

.5 = e^(-1/C)

ln(.5) = -1/C

therfore...

C = -1/ln(.5)

C = 1.443 F

thats why people use active components, would you really want to buy a 1.4 F cap just for that?