fire harness

[Steve Hess]

Not a typo. My small block 65 coupe caught fire today. Luckily I carry a small fire ext. and got a hold of it. If you don't carry one GO BUY ONE TODAY!

I was driving and the engine quit dead - no ignition. Then came the smoke. (then fire) It appears that the red wire from the installed Pertronix electronic ignition module that goes to the ballast resistor shorted and caught fire. As
many of you may know the Pertronix uses this wire from the positive coil / ballast side in addition to the black wire from the negative side of the coil. This red wire melted into three pieces. Further examination shows that
the wire going from the ballast to the ignition switch was now in bad shape too. I followed it through the firewall and under the dash. This wire has melted insulation through out. It is obviously time for a dash pull and
dash harness replacement.

It looks like the red Pertronix wire was the culprit, however has anyone else had a similar experience? Could it be the ignition switch or fatigued dash wiring or a bad firewall block or what?
Now for repair. Are there things I should do or look for while I have the dash out? Everything worked on the dash except the ammeter. I think the meter itself is bad, Also the dash light are very, very dim.

Any opinions will be appreciated,

[Duke W.]

Re: fire harness

The only reason wire insulation would melt and catch fire is because something in the primary ignition circuit shorted and caused a big current overload. It's never been clear to me how these Pertronics units are wired, but the only resistive devices in the single point primary ignition circuit are the coil and ballast. The ballast would be very unlikely to short, and the same goes for the coil. The nature of their construction is that if they fail, they will almost invariably fail OPEN, not short. A shorted condenser would just short the points. The engine would not run, but it wouldn't overlaod the circuit.

Since the Pertronics unit requires power to operate, it too could short and cause the problem you experienced. From your description, it sounds like the Pertronics unit shorted and almost set your car on fire. You should be able to determine where the short is with a good ohmmeter. Let us know what you find as this could be a warning to those with these aftermarket electronic point replacement units. I'm not a big fan of them, and I suggest you go back to points. Use the high breaker arm tension points if your redling is above 5500.

Duke

[Jack H.]

Re: fire harness

"Something" drew too much current causing the wires to smoke. Now that the damage is done, it'll be VERY hard to find/blame the culprit without a forensic electric engineer. But, you can conclude this much....

When there's a short, current follows the branch wiring path of the short. Putting it simpler, if the fault had been upstream of the ignition module (in the dash/ignition switch harness area) you'd expect only that portion of the wiring to show immediate damage from excess current. Since the engine compartment wiring associated with the ignition system's primary (low voltage) side smoked/melted, the odds are VERY high this portion of the wiring was involved in the fault!

The older design solid-state ignition modules intended as drop-in replacements for conventional Kettering ignition (points), ARE known to have a few Achille's Heel performance issues. Things like what happens to the SS module if you accidentally reverse bias it (low battery, take a jump from a friend and accidentally criss-cross the jumper wires)?

In my book, the folks at M&H Fabricators, really burned designer midnight oil in due diligence with their Breakerless SE system! Though this single wire, drop-in ignition module was a 'Johnny come lately' to the crowd (Mallory, Pertronix, Etc.), discussions with M&H's President/CEO, Tom Marquez, IMPRESSED me with the feature/function content they crammed into their product as well as its system level fail-safe content. Having been a design engineering manager at Texas Instruments and telecom company engineering VP, the Breakerless SE is what powers my classic driver Corvette....

[Steve Hess]

Re: fire harness

Thanks for your input Duke and Jack.

Well, good news. I took out the dash and found that the only wire in the dash harness that fried was the ignition wire. Relatively easy to replace without cobbing the harness. The other offending wire was the power wire to
the Pertronix unit. I really appears that this wire shorted allowing the ignition wire to take the load and overheat. The real question is did the the Pertronix wire overheat first and melt the casing to expose the bare wire and
short to ground or did it short first through friction allowing it to ground and overheat.I intend to replace the toast wires and fire up the car without the dash panel in place to see if the same wires heat up again.
It's difficult not to go back to points given the hassle that this has been. I don't drive hard or that far. The
Breakless SE system sounds good, but I might as well keep the Pertronix in place if I'm going to do that and SHIELD THAT WIRE!

At least while it's apart I can replace the ammeter. It's dead. Any suggestions where to find one?

[Jack H.]

Re: fire harness

Original dash guages USED to be in all the catalogs. Now, they've pretty much dried up and what is available is EXPENSIVE! Consider pulling your ammeter and sending it to one of the houses that advertizes instrument restoration in Driveline or simply search the archieves here for reports of what service folks have used & liked....

[William C.]

Re: fire harness

Have you checked the gauge itseelf for function and eliminated all the other "standard" cuases of ammeter "inop" such as the conection between the pass compartment and the engine harness?

[John H.]

Re: fire harness

I'd bet that the spade connector on the (+) coil terminal was positioned such that it touched the inside of the upper ignition shield and shorted there to ground - that creates a dead short through the ignition feed and fries the ignition harness right back to the ignition switch, as there is no circuit protection on that ignition feed until 1967 (fusible link at the starter). I've seen this exact same failure mode at least five times in the last ten years; the (+) coil connection looks pretty innocent out in the open, but when you install the top shield and push it down to align the holes, it's VERY easy to create a dead short unless the coil is positioned in the bracket such that the (+) terminal is located AWAY from the inside of the upper shield. Makes lots of acrid white smoke, can start a fire under the instrument panel.

[steve hess]

fire harness - Wow

John,

That's the kind of info I wanted. I'll be running home to check the ignition shielding for an arc mark. I definitely need to find an insulting cap for that connector.
As for the ammeter, I have tested the gauge independently and it is broke.
I found a refurb replacement at the local Corvette shop. $69.95 + core.
Long Island Corvette has the licensed GM repro for $79.00.

Thanks,

Steve

[Steve Hess]

fire harness - cause and cure

John Hinkley pointed me in the right direction. It wasn't the coil spade that shorted to the ignition shield, however close inspection shows that the hot lead from the Pertronix unit was cut through by the ignition shield. That shield is very sharp on the bottom. I'm surprised that more distributor related wires don't get cut up by them. I picked up some chrome door edge molding ($4.00) and will line the bottom edge of the shielding where applicable. It appears that I can get away with just doing the back edge. Probably won't be able to see it and what you can see blends in nicely.

[Don Ursery]

Re: fire harness

I have a '62 & '66. You're input regarding coil, wires and shorts has truly opened my eyes. Thanks for all who respond to member questions. It helps us ALL.