[patrickt]

The beauty of the big capacitor connected across the positive and negative leads to the MSD box is that the capacitor allows leaking alternating current from your alternator to pass through the capacitor without ever going in to the MSD box. It also buffers the direct current spikes as well. But you have to remember to bleed your cap off when you work on your wiring. In fact, if you disconnect your battery and then hit your horn button you will hear the relay click and just a hint of a horn toot as the cap empties out. Or you can throw your light switch on as well. The original MSD boxes, along with the big cap, are very reliable.