ignition coil exploded

[Guest]

Hi There,
I'm nearly at the end of my '60 T-bird restoration.
Yesterday I've replaced my electric window weatherstrips.
I had the ignition switch in the on-position to operate the windows.
Suddenly after a couple of hours I heard a big bang from the engine compartment and saw my ignition coil had exploded ...
Afterwords I did find out the +-side of the coil had 12V when the ignition key is in the on-position. Is this correct? Or do I have some other issues? (faulty coil ...)
Best regards,
Peter from Belgium

[scumdog]

Having the key turned on for a long time without the motor running will do that to the coil - no fault with the coil,. (it can also fry your ignition points).

[simplyconnected]

I totally agree with Scumdog. This can happen at random, IF you leave the key on, and depending on whether the points are closed. If the engine stops with the points open, ignition current can not complete the path to ground. But, if the points happen to be closed, and you leave the key ON, your battery may be found dead. As you found out, the coil will overheat and may explode, but this rarely happens. Points that are 'lightly' closed will burn.

Think of it- in normal engine operation, points open and close causing a 'duty cycle'. The coil is conducting half the time and only half the heat is created. - Dave

[Guest]

Thanks guys for the help.
Who needs books if you can rely on fellow T-birders.
I already had some nightmares that I had to redo the dash electrics ...
Good lesson learnt not to leave the ignition switch on for a long time.

[jopizz]

It's best to use the ACC position of the ignition switch when you play with the windows.

John

[KULTULZ]

Correct. With the key on the RUN position (engine off), you are bypassing the IGN RESISTOR and full BAT VOLT will be applied to the IGN SYS which is rated for 9V running.

Either use ACC position or disable IGN circuit.

[scumdog]

Correct. With the key on the RUN position (engine off), you are bypassing the IGN RESISTOR and full BAT VOLT will be applied to the IGN SYS which is rated for 9V running.

Either use ACC position or disable IGN circuit.

I thought 12V only got through when the key twisted to the 'start' position and once you let go the key back to the 'run' position the current to the coil got there via the ballast-resistor?

Or have I got it wrong (again some would say!)

[KULTULZ]

I thought 12V only got through when the key twisted to the 'start' position and once you let go the key back to the 'run' position the current to the coil got there via the ballast-resistor?

Or have I got it wrong (again some would say!)

If the starter solenoid has two posts (S and I), when you turn to start, the IGN is powered up with BAT VOLT from the solenoid. When you release the key to ON, the IGN is powered with BAT VOLT through the IGN SW and resistor block/wire until the current flow heats the resistor and curtails the current flow.

Now if you leave the key in the ON position not running, the current may overpower the resistor. It states plainly in the OWNERS MANUAL to not do that...

Like Dave said, it all depends on what position the contact points are when the engine stops.

Same with PERTRONIX. Warning not to do that. That is why they came out with PERTRONIX II, because some like to listen to the radio while waiting for the old lady with the IGN SW in the ON position rather than the designed ACCESS position.

It's much like the old lady asking if she looks fat in her new dress and you say yes or hesitate.

Hope that made sense...

[KULTULZ]

Did I make any sense at all?

[Guest]

Thanks Kultulz,
It realy does explane things and as so many "stupid" mistakes ... they all make sence once you get the technical explanation about things.