Overheating ignition coil

[crankedup]

The battery on my vintage Austin 12/4 went flat overnight, I used a slave battery to get it running and all seemed fine at first.
I then noticed the engine started to misfire with one or more cylinders missing.
When I switched off the engine I noticed the ignition coil was extremely hot and remained so for about an hour. At this point I disconnected battery.
The ignition switch seems to be permenately on too??
Any ideas please???

[GreenV8S]

Normally the coil is rapidly switched on and off to produce the sparks, and isn't left switched 'on' permanently. If you stop the engine and leave the ignition on then depending where the engine stops (points open or closed) the coil may be left switched on. On a modern car the electronic ignition would cut power to the coil which stops it overheating, but on a car that age there probably won't be any fancy electronics to protect the coil. So leaving the ignition on with the engine stopped may have cooked the coil.

Couldn't say why the ignition is staying on except to say it sounds like an electrical fault, perhaps the wiring has been overheated allowing a short between 12v and the ignition circuit?

[crankedup]

Thanks GreenV8S, the ignition switch is a simple thing with no key required, to the left it is off and down it is on. It now seems to be on whichever postion the switch is at. The coil is pulling current continuesly.
Looks like my drive out to Mid Essex TVR meet is off

[steve_D]

crankedup said:

Thanks GreenV8S, the ignition switch is a simple thing with no key required, to the left it is off and down it is on. It now seems to be on whichever postion the switch is at. The coil is pulling current continuesly. Looks like my drive out to Mid Essex TVR meet is off

For the time being just put another switch in the line or pull a terminal off.
While your doing that the coil should cool and may be none the worse for it.
If left on for even a short while they can get hot enough to burn your hand.

Steve

[crankedup]

Had a day on it and still no further forward, so its into my local garage for the cure and new coil, points and condenser.