Do not waste your time on a cap. You do not have a large draw of electrical on your car to even warrant one. It is a good idea. But think of it like this. If you did have a big stereo in the car and was worried about it not keeping the supply of power to the msd and other stuff because of the boom, than you would do the cap for the stereo.
I think you will be fine with just grounding it to the battery and running it like normal.
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