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what does it mean when ign. coils take an external resistor?

Started by Brett, June 25, 2006, 04:04:31 PM

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Brett

What does it mean when a coil says it takes an external resistor?

I recently put in a chrome accel superstock in my 71....been running like gargage since. I just bought a $12.99 Borg Warner coil and there is a big note on it that it takes an external resistor..what does this mean?

Thanks,

Brett

Doug Houston

Quite a few ignition coils can be damaged (burning up) if the ignition is left on wihout the engine running. The use of a series ballast resistor keeps the currnt down under those conditions. Most, if not all 12 volt ignition systems have either a resistor mounted somewhere in the engine compartment or its resistance wire built in the harness. When running, the coil sctually runs on about 8 volts.

The starter solenoid has a shorting switch on some cars, which shorts out the ballast resistor while the starter is running.

Brett

Thanks for your reply. Do you know if a 71 472 has an external resistor? The coil I purchased (from a reliable parts source, but I am compelled to check nonetheless) states that it is for use with an External resistor.

Geoff Newcombe #4719

Brett,
Do you have the 1971 Shop Manual for your car?  If so, read on page 6-25, item d. and ignore the rest of this post.  If you dont have the manual, the part of d. relating to your question reads as follows ......

A resistance type wire is connected from the ignition switch to the ignition coil in the primary circuit.  This RESISTOR (my caps) reduces the voltage at the coil from 12 volts down to a range of 8 1/2 to 10 1/2 volts under normal operating condtions.  To insure adequate ignition voltage during the engine cranking period, the resistor wire is by-passed by a feed from the starter solenoid, and full cranking voltage is supplied to the ignition coil during this period.

In other words, yes, the 71 472 does have an external resistor in  the form of the resistance wire mentioned above.

If you dont have a 71 Shop Manual and would like to have one, I have an extra one in very nice condition for $30 plus shipping.

Brett

Thanks!

Thank you very much for the info. I do have a shop manual in good condition (subjective of course:) ),

bad enough condition I can leave it with a mechanic,

but nice enough I warn him it is a fragile old book.

I would love to have one in near mint condition as a second copy...dont ask me why..

As a side note,
a new coil, new plugs, and a new distributor (shoot only $55 reman from Cardone!) solved my problems. Turns out the timing was wayyyyy off so this must have played a part too!  Thanks again!