Coil wiring

A

alk

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Over the winter I had the motor rebuilt for my ski boat. Sbc, mostly indmar, pretty simple.carb motor with Mallory electronic ignition, no spark, and I seem to be having a problem getting 12 volts to the coil, and surprisingly the problem is with the negative side - it's losing two volts somewhere.

There are two wires on the negative terminal - gray which goes into the harness, for the tach I assume.

And green which comes from distributor. The distributor shaft appears well grounded, and shows 12 volts when I put the - lead from the volt meter on it. But the wire to the coil from the distributor doesn't carry the full voltage.

Any idea what could be going on here, and best way to fix? Was considering running a wire from coil neg to a good ground, but maybe I have an issue that needs to be addressed?
 
Check the main ground strap. I think it runs from the starter to the battery. Make sure its clean and tight.
 
The motor is grounded solidly, as is the distributor. But the wire from the distributor to the coil negative seems to be a problem. I suppose I need to figure out what is up inside the distributor, and see where this wire makes its way to ground.

this is a pretty common ‘old school’ ignition system, so was wondering if anyone knew how the coil Negative terminal was typically grounded?
 
OK - just thinking out loud. Isn't the ground wire from the distributor controlled by the ignition module? Think of the old points system. When the points closed, the circuit was closed and the coil was "told" to fire. If my memory is correct perhaps you have a bad ignition module? If my memory is not correct, sorry for wasting your time ;-)
 
you may be onto something, as I believe the old versions did ground via the points. perhaps my occasional lack of spark has nothing to do with the voltage on the negative coil terminal, and I'm within spec here.

I saw some youtubes on how to test the module, but they aren't making much sense. If I have to replace this $60 module, I may convert to the Merc Tbolt4 ignition I have sitting in my garage. that's a lot of wiring splicing though. and the merc tune up parts aren't cheap. But it's probably a better ignition system.

Looking into this some more, seems my module is indeed shot. I believe it is Supposed to cycle below 3 volts, back up to 12 volts as the distributor spins. Mine is jumping from around nine to twelve. Not good,
 
You dont have a resistor in the circuit from the old system do you?
 
No, at some point in the past the mallory distributor was upgraded with an electronic module, to replace the points, and new coil put in. as per mallory documentation, no resistor needed.

My test was not valid, the negative terminal on the coil is not a constant 12 volts. Most every other electrical system has constant negative, and switches/varies the positive. What I forgot, or maybe never knew , is that ignition works by pulsing the negative to the coil.
 
Still have not decided what to do with this ignition, it’s been flaky the entire time I’ve owned this boat. General consensus of the online reviews is that the ignition modules are either complete junk, and need to be replaced every few hours, or the modules are ok, but they can’t handle the most mild voltage surges, so unless your electrical system is pristine, you will have problems.

So i have a few choices -

I’ve got a merc thunderbolt 4 sitting in my shed - for about $100 for new cap, rotor, wires, coil, i could be back up. But the thunderbolts scare me - as the ignition modules are like 700 to replace. Mine might be fine, but if I ever need to replace, that would sure suck,

Michigan motors sells delco voyager marine replacements - new distributor, more modern coil, wires, everything. And cheap parts delco tune up parts going forward. But I only paid $250 for this boat, so hate to drop 500 on a tune up!

Hardin has a ‘performance kit’ for 399 - but it’s with the old school oil can coils, which never seem to last.

Choices.....
 
Thanks. I ordered that part from summit yesterday, should be here today. But the online reviews say the same thing I have experienced - this part does not last very long.

If I burn another one, going to pull out the ignition and start over with something else. Or might redo it even if I get this working. Looking for best alternatives if I start over.

Not a real radical motor - Small block Chevy, Weber 4b carb, vortec heads, comp cam w/ hydraulic flat is bit “bigger” than stock, dished pistons. So I don’t need a $1500 msd 9k rpm ignition. Just something that performs decently, and most important is more reliable than what I have today.
 
overvoltage and loose grounds burn up electronics. There should be no issue running a resistor on the + side of the coil and module
click to enlarge
 
According to some tech article I saw online, these modules don’t do well with ‘one wire’ alternator setups - as this design sends voltage spikes every time you shut the motor off. If true, that would explain why i fry these things so fast.

Delivery came today, and motor gets spark now, and starts right up. Knocking a bit, but I‘ll mess with it some more if we get another day without rain.
 
I think the Mallory conversion kit , like the original Pertronix "Ignitor" kit with the black module, does say to retain any ballast resistor that was used with the points and condenser setup.
And, like the the original black "Ignitor", I believe I've read the Mallory conversion module is susceptible to burning out if the ignition key is left in the On position but engine Off for a little while.

FWIW- The better, more robust Pertronix "Ignitor II" with the red module does NOT retain the ballast resistor and does not burn out due to leaving the ingnition On/engine Off.

That said , I haven't used either conversion , preferring instead on my previous set of blue carbed 5.7L I/Bs to swap the worn points distributors for the really good Delco Voyager EST electronic ( including all-electronic advance) distributor kits with matching coils and coil /plug cables.
Those distributors were the best marine distributors I ever had , -flawless for the remaining maybe 6-7 yrs I had those engines. (I'm not sure if they still use the same Delco EST distributor in the present Voyager kits though.)

The Voyager EST kits were very highly recommended to me by the head factory tech at Crusader, and my big winter boatyard installed about a 100 of them on the older engines.

Good to hear your engine runs again , and hope you get that knock under control very quickly.
 
That's the kit, just has newer type distributor & coil than my old ones. M Mtrz is one of the few remaining sources for the Voyager kits.
Not likely a concern if you have a single standard LH, CCW rotation I/B , but just note the kit for the opposite-rotation RH engines has a different distributor setup and is about an add'l $100. I had one of each.

Price looks to be about the same as the ones I purchased back around 1997 or so. The yard installed mine.
 
Darn it, fried ANOTHER Mallory module. And I’m on vacation, with the boat, and limited options for replacement., should have done the delco upgrade last spring, I wonder if Napa will have points that will work with the Mallory yl distributor, to salvage my week. Probably not. I think this boat has finally beat me.
 
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