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Discussion Starter · #1 ·
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).
 

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Only had one failure with MSD in 15 years with four boats running MSD ignitions. The failure was caused by a bad ground, and yes he box went up in smoke. MSD inspected the box, said it was a 6M-2 and was sealed, MSD said it was not repairable, it was way out of warranty, but they stepped up and exchanged it for $85.00
 

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Did this boat have some wiring issues before? Or is all of the wiring new!
Most issues with MSD that I have had have been ground problems! WT:)devil

MSD Is not a bad company to deal with and do stand behind their products!
 

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Discussion Starter · #6 ·
Did this boat have some wiring issues before? Or is all of the wiring new!
Most issues with MSD that I have had have been ground problems! WT:)devil

MSD Is not a bad company to deal with and do stand behind their products!

I wired it earlier this season...no problems whatsoever so far.

It's getting rewired again since there is some damage from the small wiring fire. It's not much...just an ignition system and a couple of gauges
 

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Discussion Starter · #8 ·
I thought of that, but the 2 big wires were not bundled with anything...they were cut to length and run straight to the battery about 10" away. I had the box mounted up under the gunnel directly in front of the battery...the wires were not tied up to anything as it was such a short run, they stayed suspended by themselves. The rest of the harness runs on top of the MSD box underneith the gunnel and was in one of little flex conduit things. All the other wires exit the other side of the box so they joined into the conduit at an earlier point. of course, the conduit and insulation was melted..still there, but melted. No signs of burnage anywhere near as severe as the 2 big ones.
 

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are you runnin a blaster 2 coil or another coil? if you're runnin the lil red solid msd coil, that's what is burning up your box, those coils are only for 7a boxes.
 

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I understand the coil taking down the box, but it doesn't explain burning up the main power feed wires.
pulled to much current. i've gotta 6al open right next me now about to replace a transitor due to a coil shorting out;) had to order the transitor from the local radio shack but it was only 56cents:D the 6a has the lil fused circuit near the transformer, these 6al's don't have that, they burn up transitors. think of it as a radio amplifier , cause that's all it is, amplifies the incoming signal. if you put to much load on a radio amp, it'll shut down into protection mode, a msd 6al will just keeping trying to work till it smokes something.6a will just fry the fused circuit on the board, those can be fixed easily with lil string of wire and solder.6a's also fry that fused circuit when they get wet. can't tell ya how many boxes i've fixed for buddies gettign them wet
 

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Discussion Starter · #12 · (Edited)
I'm running a blaster 2...

So, is there a better alternative? I've got no problem running an HEI with an upgraded module but I'd like to have a rev limiter....and the HEI won't fit with my tunnel ram.

EDIT: come to think of it, I replaced the coil when I put the new box in on Saturday morning...cuz I'd "loaned" my old one out the night before. I'll test it.
 

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mo balls than $cents$
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I'm running a blaster 2...

So, is there a better alternative? I've got no problem running an HEI with an upgraded module but I'd like to have a rev limiter....and the HEI won't fit with my tunnel ram.

EDIT: come to think of it, I replaced the coil when I put the new box in on Saturday morning...cuz I'd "loaned" my old one out the night before. I'll test it.
has the coil ever been changed while you were changing msd boxes? i've seen a blaster coil short internal and smoke a box before, its not that uncommon. remember the ole days when these type of coils would overheat and blow up:D well the msd blaster won't blow up but it will swell and short internal.

honestly i've never had a box of my own go completely bad. i've had 1's that worked intermittently but that was always the solders on the board for the heavy gauge black and red wires being cold soldered to the board and cracking. all ya gotta do there is apply fresh rosin core solder to fix that.
 

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Discussion Starter · #14 ·
has the coil ever been changed while you were changing msd boxes? i've seen a blaster coil short internal and smoke a box before, its not that uncommon. remember the ole days when these type of coils would overheat and blow up:D well the msd blaster won't blow up but it will swell and short internal.

The coil was new when the second box went in....hard to understand though how a coil could cause a dead short across the main leads.
 

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mo balls than $cents$
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The coil was new when the second box went in....hard to understand though how a coil could cause a dead short across the main leads.
have you ever played with subs and amps? ever bridge a amp and put too much load(put a 1ohm speaker, on a 2ohm stable amp) on it, just to see if shutoff when you turned up the volume? or have you ever felt the leads off a amp? msd box is basically the same circuitry, but without the auto resetting protection built in. it can pull so many amps that the lead sheilding can melt.

i'm just sayin there's something wrong here , msd boxes don't fail that often, there's gotta be wiring issues or something that needs addressing if you're steadily goin thru boxes.
 

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it can pull so many amps that the lead sheilding can melt.

i'm just sayin there's something wrong here , msd boxes don't fail that often, there's gotta be wiring issues or something that needs addressing if you're steadily goin thru boxes.
I agree something is very wrong here. But I don't see how you can melt the insulation off the main power feed with out blowing the internal fuse.



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mo balls than $cents$
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I agree something is very wrong here. But I don't see how you can melt the insulation off the main power feed with out blowing the internal fuse.
6al doesn't have the internal fuse, i've got 1 right next to me open, i just fixed it few minutes ago. the transistor in it is what took the heat. 6a is the only msd box i know that has the lil shorting circuit that melts if the box has gotten wet or the coil leads were shorted(or coil shorted). you can just pull a strand of wire outta a 18gauge wire and lay it across, solder it in on the 6a's to fix em. wish the 6al had it too, we'd see less of them in the garbage.
 

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Mag box

I've never had a Vertex mag box go bad, or smoke wires.......Oh, wait, Vertex mags don't have boxes..:D:D........And they fit with every tunnel ram I've ever seen.......Sorry, I just had to throw that out there.......Ray :)hand
 

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mo balls than $cents$
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I've never had a Vertex mag box go bad, or smoke wires.......Oh, wait, Vertex mags don't have boxes..:D:D........And they fit with every tunnel ram I've ever seen.......Sorry, I just had to throw that out there.......Ray :)hand
haha ray, try runnin a retard or delay on it:D
 
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