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MG MGA - Coil left on

I'm rather ashamed to say that after fidling with my MGA I left the ignition on and only discovered it after about 5 hours. The coil was hot but touchable. Not sure if this equates to 'baking' but I've heard accounts that a coil left on can be ruined due to insulation failing. Seems to be working still but I wondered what the prognosis might be?
J H Cole

If you left the ignition key on for 5 hours, and the contact points in the distributor happened to be apart (i.e., open), then I would say that no damage was done as the ignition circuit was broken. I'm sorry to say that if the contact points were closed, then your coil is caput. It will not withstand 5 hours of continouos current passing through it.
You have to be very lucky to switch off the ignition with one of the lobes on the dist shaft to stop at the open points position. Unless of course you had previously turned the engine by hand, in which case there is a probability that you may have stopped the turning at the point when the points were open. It's a gamble. I would keep a spare coil in the boot if I were you, as your existing one might let you down unexpectedly.


F Camilleri

Hot, but touchable, puts the case of the coil at around 150-160 deg F, at least for me. The coil can handle a lot more than that, depending on the grade of wire used. Even average grade magnet wire insulation is rated for 260 deg C. Today's ignition coil wire is probably made from even better stuff.

What you did is a common mistake. I'd be surprised if the mfgrs did not consider this common situation in the design of the system even way back then. This is proven by your observation that it still functions properly.

Even if you are still good, I'd keep a replacement coil with you. I've had a brand new coil fail in about 1000 miles so I carry a spare all the time. I'd put the new one in service and keep the old one as a known good spare to get you home just on general principles.

Chuck Schaefer

This thread was discussed on 15/12/2009

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