car audio, led’s to subs?

Ok I'd like to hook up some l.e.d.'s to each of my subs that will light when they are properly connected. How would I go about doing this? I know that the sub wires have fluctuating voltage and that l.e.d.'s can't handle 12v so they need to be stepped down with resistors...any input would be appreciated. Thanks in advance

Figure out the voltage across the sub. V = the root of Pwr divided by Resistance. EG if 400W into 1 Ohm, V = √400 = 20V. Hence try ~10 x 2V LEDs or ~6x 3.4V LEDs or add resistors for less LEDs or if you want too. The above assumed RMS power, but it probably won't make much difference. The LEDs will tolerate higher than their nominal current because they can, and because its not a DC current.

I'm not sure I fully follow you. How did you get 20 out of 400? I understand how to find voltage drop, amps, resistance, watts and voltage but what I don't understand is how do I know what the l.e.d.'s can handle power wise and also if the fluctuating current to the subs will affect the l.e.d.'s (dimming and brightening)

That's what I gave above - how power varies with voltage and resistance. It is a combination of V=IR and P=VI, hence P=VxV/R = IxIxR. (Ohms, Volts, Watts, Amps) 20 squared = 20 x 20 = 400. The square root of 400 = √400 = 20. If you have 20V RMS into a 1Ω sub, the sub's power is P = VV/R = V-squaRED / R = 20x20/1 = 400W. You merely need to match the LEDs' voltage-wise to the sub - eg, the LED series string must handle the max voltage of the sub. FYI - a LED's resistance is much larger than the sub (eg, typ 100Ω) so n LEDs in series will be n x 100Ω hence even larger so their power consumption is negligible nothing compared to the sub (or most speakers).