Engine is a BBC w/ MSD distributor using an MSD (6420) 6AL CD/amplifier box.
If you’re not familiar with them, here’s how they’re wired…
#12 Red – main power, direct to battery
#12 Black – main ground, direct to battery
#16 red – key hot
small purple/green - input from dist. Mag pickup
small orange/black – output to coil
1 white wire - input from breaker points (unused in this case)
1 yellow wire - input from timing computer (unused in this case)
Pretty simple right?
Box number one crapped out after 4 weekends…just quit. Confirmed powers and grounds, disconnected input wires from dist, key on and tapped white wire on ground (to simulate points operation) and had no spark….condemn the MSD box.
Got new box and wired up same as old box….fired right up. Ran boat for about 1 hour then sputtered and quit. As soon as I touched the key the restart…lots of smoke and small fire. Inspection revealed all of the insulation burned off of the main ground wire, and all off of the main power except for about 2 inches nearest the box. (MSD states to hook these two wires up without fuses..)
The battery is about 10 inches away from the box, there is nothing metallic between the box and the battery except a stainless braided fuel line and some nicely anodized AN fittings which the wires ran abotu 4 inches below, and there are no signs of arcing after a very close inspection.
MSD tech (during their “testing and repair” process) told me that the wires were just burned…they’d replace the wires and send it back to me..told me one of the wires must have rubbed through on something becuase the box worked fine. I told ‘em ****off and give me a new box.
My reasoning is that if, like they state, the main hot wire rubbed through to something grounded it would have burned from that point back to the battery. The fact that it apparently burned from the battery, through the box, then back to the battery up the main ground tells me that it must have a short inside the box. I didn’t want to “duplicate the problem” by hooking up the 2 main power/ground again and then powering up the key circuit to test for continuity for fear something bad might happen. I know the wires didn’t rub through to the opposite battery terminals because they were both melted into the battery about 2 inches away from the terminals.
What do ya think? I wasn't about to put that box back in the boat, and I'm contemplating not putting any of those boxes back in the boat...at least not without fuses (which MSD states not to use).