Electrical Help

[astat1]

Greetings all,
Hoping someone can chime in to assist.
My 1969 GT500/C6 stumbles under load only when engine is hot. Runs fine at temp in park/neutral but dies in drive when hot. The only mod is a pertronix 2.  All gauges function, including tach.
I changed out multiple yellow top coils and now have tried a Flamethrower coil. I am pretty ignorant with solving electrical issues, but can post what I know.
The coil is getting 12v at start but goes down to 10.6 on run. I realize that the resistor wire may be an issue (I have read the voltage should be 6-8v on run) with too much for the yellow top but not for the flamethrower (prefers 12v). When the ignition switch is bypassed (coil to battery) the stumble issue is resolved. The stumble is also resolved with a direct bypass from ignition C terminal to coil. The issue is not resolved with bypasses of the first 2 connectors off coil (? part numbers 14289 and 14L290 as listed in the 1969 Shelby Shop supplement).
Can the tach be the source of my issue even if it's functioning? Why would the issue be temperature sensitive? Any comments appreciated!!!
Thanks

[Bob Gaines]

Greetings all,
Hoping someone can chime in to assist.
My 1969 GT500/C6 stumbles under load only when engine is hot. Runs fine at temp in park/neutral but dies in drive when hot. The only mod is a pertronix 2.  All gauges function, including tach.
I changed out multiple yellow top coils and now have tried a Flamethrower coil. I am pretty ignorant with solving electrical issues, but can post what I know.
The coil is getting 12v at start but goes down to 10.6 on run. I realize that the resistor wire may be an issue (I have read the voltage should be 6-8v on run) with too much for the yellow top but not for the flamethrower (prefers 12v). When the ignition switch is bypassed (coil to battery) the stumble issue is resolved. The stumble is also resolved with a direct bypass from ignition C terminal to coil. The issue is not resolved with bypasses of the first 2 connectors off coil (? part numbers 14289 and 14L290 as listed in the 1969 Shelby Shop supplement).
Can the tach be the source of my issue even if it's functioning? Why would the issue be temperature sensitive? Any comments appreciated!!!
Thanks

Pertronix should have 12V to it . If not then strange things may happen.  If you run 12 volts constantly to a factory yellow top coil it will overheat and fail given enough time at 12V. If you bypass the resistor wire so that the pertronix works like it is supposed to yuu will have to change your factory coil to a aftermarket style that can work on continuous 12V.  Of course you can always run factory points and a factory or aftermarket coil and not worry about the bypass wire like millions of Ford products have done over the years.

[69 GT350 Vert]

I flipped my tach connector around and ran a dedicated black wire the to pertronix to bypass the pink resistor wire.  Its been working.  See thread link below.

https://www.saacforum.com/index.php?topic=6850.msg58085#msg58085

[Bob Gaines]

I should mention that most after market coils have a resister built into them so they can run on straight volts or the variable voltage supplied by the factory resistor wire. A factory yellow top coil does not have a resister built into it so if 12 Volts is supplied continuously it will heat up and eventually fail . Sometimes when they fail it is quite dramatically. They can explode and make a mess under the hood . The oil used inside them is carcinogenic too. 

[69 GT350 Vert]

I always run the matching pertronix coil to the pertronix module.  As Bob said, don't run 12V to a stock coil - it will fail.  I found that out. 

[FL SAAC]

I flipped my tach connector around and ran a dedicated black wire the to pertronix to bypass the pink resistor wire.  Its been working.  See thread link below.

https://www.saacforum.com/index.php?topic=6850.msg58085#msg58085

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