Ignition switch wired wrong?

Hi all,

my '71 M code Mach 1 has a Flamethrower coil that needs an external resistor, so it's hooked up to the standard ignition wire (or so I think) which supplies around 6V - all good there.  However I've noticed that this wire is 'hot' with the key in the accessory position as well, which I believe shouldn't be the case.  The same goes for the full 12V supply wire coming out of the same section of the loom which is used for the electric choke, meaning the choke element is 'hot' in the accessory position as well.

So am I correct in thinking things are wrong here?  With the earlier year Mustangs I've owned the coil wires have only been energised in the start and run key positions, so does this mean someone has wired up the ignition switch incorrectly at some stage?

I have copies of all the wiring diagrams so if anyone can point me in the direction of both resistor and full 12V supply wires in the engine bay that are only active with the key in start or run position that would be a big help!

Hi all,

my '71 M code Mach 1 has a Flamethrower coil that needs an external resistor, so it's hooked up to the standard ignition wire (or so I think) which supplies around 6V - all good there.  However I've noticed that this wire is 'hot' with the key in the accessory position as well, which I believe shouldn't be the case.  The same goes for the full 12V supply wire coming out of the same section of the loom which is used for the electric choke, meaning the choke element is 'hot' in the accessory position as well.

So am I correct in thinking things are wrong here?  With the earlier year Mustangs I've owned the coil wires have only been energised in the start and run key positions, so does this mean someone has wired up the ignition switch incorrectly at some stage?

I have copies of all the wiring diagrams so if anyone can point me in the direction of both resistor and full 12V supply wires in the engine bay that are only active with the key in start or run position that would be a big help!

Click to expand...

bac, just checked my 71 fb/ wo gauges and No it should not.

Someone could have re-wired it , OEM chokes rely on the stator wire from the charging system, most aftermarket chokes need to see 12 volts to operate correctly.

 some aftermarket distributors require 12 volts in the run position, which our cars did not provide because there is a resistor wire to drop the voltage down.

You did not state what type of distributor you have, perhaps a previous owner tried by-passing the resistor circuit and picked the wrong point to (tap into for power to the coil).

BoilermasterL

just checked my 71 fb/ wo gauges and No it should not.

You did not state what type of distributor you have, perhaps a previous owner tried by-passing the resistor circuit and picked the wrong point to (tap into for power to the coil).

Click to expand...

Thanks for confirming.  Distributor is a stock type with a Pertronix Ignitor 1 module and matching Flamethrower coil.  Voltage at the positive terminal of the coil is 6 to 7V and the car runs OK.   

It's looking to me very much like a previous owner has mis-wired the ignition switch at some point so I'll see what I can work out there.

Are you expecting any permanent damage to the engine from this, Brian?

Are you expecting any permanent damage to the engine from this, Brian?

Click to expand...

No, at the moment I'm being careful not to use the accessory key position to avoid potential damage to the coil and/or flattening the battery.

Would be nice to get it sorted out so I don't have to do this, and from the posts so far and the wiring diagrams it seems most likely either someone has messed with the wiring or I have a faulty ignition switch.  My gut tells me it's more likely to be the wiring: the behaviour I'm observing is consistent with someone bridging the accessory (297) and ignition (16A) wires, most likely where the ignition switch plugs into the main wiring loom.

Frustrating thing is the car has been at the mechanic's over Easter and I won't have it back for a couple more days yet...

So the car is back from having the C6 auto overhauled (no more leaks!) and I've had a chance to look under the dash.  Turns out the ignition wire from the plug connecting to the ignition switch had broken and the previous owner decided that rather than repair it, took the accessory wire and connected that to the point where the original ignition wire would have gone.  He'd also run an extra wire from this point to power the electric choke.

This is why both the ignition wire and choke wire were 'hot' in both the run and accessory key positions.  This has now been put right and the ignition wire is no longer powered in the accessory position.  Thanks to a diagram kindly provided by Ken (71fast), I used the factory throttle solenoid wire (#640) as a switched 12V source to power the electric choke.

One further question for the group: if at some stage I wanted to convert to a modern full HEI distributor with integrated coil, is there a way to do this and still maintain operation of the factory tach?

Yes you can, but it’s a lot easier to go with the Pertronix I or II ignition module. They go right in the stock distributor and then you don’t have the huge ugly hei distributor. And I think you may have to rework the air cleaner base to make it fit, but not sure. Others here have done this conversion, so they can tell you what you need to do. Or go to the search tab on the upper right area of this page and there’s probably a few previous threads on how to do it. Good luck!

Yes you can, but it’s a lot easier to go with the Pertronix I or II ignition module. They go right in the stock distributor and then you don’t have the huge ugly hei distributor. And I think you may have to rework the air cleaner base to make it fit, but not sure.

Click to expand...

Thanks John, did some looking and seems like you're correct about fitment issues with HEI units.  I have a full ram air setup including air cleaner and base so probably better off sticking with the original.  There is already a Pertronix module fitted so I'll leave well enough alone.

One further question for the group: if at some stage I wanted to convert to a modern full HEI distributor with integrated coil, is there a way to do this and still maintain operation of the factory tach?

Click to expand...

"Modern HEI", you mean 1970's tech GM stuff? Don't, just don't. This is from a guy who has driven a half dozen 70's and 80's GM trucks, most of which had the HEI setup. To maintain the factory tach in that setup, you'd need an 8920 MSD tach adapter for another $80.

A much better alternative is the Ford Duraspark I setup, which is the red grommet control box and it's matching high output coil. It was used in 77~79 302-V8 California applications.

As you have a 351C, pretty sure you can source a Duraspark distributor locally in Australia. Doesn't really matter which one, I would suggest an advance curve kit for 20° of mechanical advance in by 2500RPM. You may need to modify the advance slot to limit it to a 10L width (.410" / 10.4mm)

http://www.reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.html

Spectra Premium sells a nice new one at Rock Auto. Not sure how their shipping is to AU.

SPECTRA PREMIUM FD03 https://www.rockauto.com/en/moreinfo.php?pk=6283431&cc=1123197&jsn=5096

The "good" Duraspark setup for 77-79 302 California emissions red grommet unit with it's matching coil

Box: STANDARD MOTOR PRODUCTS LX210 https://www.rockauto.com/en/moreinfo.php?pk=49690&cc=1129980&jsn=5030

Coil: STANDARD MOTOR PRODUCTS FD477 https://www.rockauto.com/en/moreinfo.php?pk=47258&cc=1129980&jsn=5041

You can rob a harness out of any Duraspark equipped car in the junkyards, make your own with Weatherpack connectors, or buy one of the conversion harnesses.

https://www.amazon.com/Painless-30812-DuraSpark-Ignition-Harness/dp/B00062ZZ16

George Pence did an extensive writeup on the Duraspark units over at the Pantera forum.

https://pantera.infopop.cc/topic/parts-needed-to-convert-duraspark