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MG Midget and Sprite Technical - No Ignition light - hot coil

72 midget coming back out in the spring -- no ignition light (bulb and connections fine) though it starts ok. Then noticed the coil is getting V hot simply with the ignition being switched on ...
Not sure what to check, is this likely to be a failed coil or some other issue ?

Any suggestions welcome ....
Kevin
K Davies

Kevin

Normally, the coil is passing current around 2/3 of the time - this is when the points are closed. It therefore becomes reasonably hot when the engine is running.

When the engine is stopped with the ignition on, and the points are close, the coil will become hotter still; possibly may become damaged, as now current flowing the whole time. [If engined was rotated to points being open, of course the coil will be ambient temp.]

So you may not have a problem.

The ignition light is powered by the ignition... and the bulb comes on when the control box takes the dynamo out of circuit as it's not producing enough volts to charge the battery... so you may have a problem with the control box... (assumimng your' 72 have dynamo still fitted).

A
Anthony Cutler

Yes Anthony is spot on, the coil will get hot and is nothing to do with your problem The ignition lamp is a function of the voltage regulator (control box) or the alternator if that is fitted.
Robert (Bob) Midget Turbo

Thanks for that, makes snse. There is an alternator fitted so I guess this is where the problem lies. I've just never seen a problem like this - I can measure a voltage at the ignition lamp holder of about 13v when the key is turned "on" but it will not light the lamp (which is in good wkg order) & this makes no sense to me?
Any further comment welcome
Tks
Kevin
K Davies

Kevin

One side of the ign bulb is connected to +12v ignition; the other goes to the alternator. It's the thin wire that isn't brown(!)

You might check the continuity of this wire by turning on the ign with the alt plug disconnected: then you'll measure the same +12v from the bulb at the alt end.

If that's OK, it suggests a fault in the diode pack of the alternator.

If the alternator is charging OK, ie. you have 13.5v or more at the battery when the engine is at fast idle, you can stop worrying and learn to live without an ign lamp; if the alternator isn't charging, you need a replacement.

A
Anthony Cutler

As usual I will refer you to Paul Hunt regarding the ignition light. Read this
http://www.mgb-stuff.org.uk/electricstext1.htm#theory
Mike Howlett

Hi, I am also experiencing a similar problem on my 74 reg round wheel arch 1275 midget, in error I left my ignition on for about an hour when my midget wouldn't start, when I went back to try and start it again there was a hot electrical smell and the coil was very hot, I have now no live to the coil and points, has anyone any ideas how I can sort it out?
P Thompson

P Thompson - whilst you're waiting for an answer - do you know for sure that your not getting a live supply TO the coil and points, have you metered to check?

I left my ignition on by mistake for at least 12 hours without harm but I don't have points
Nigel Atkins

Thanks Nigel, I checked for a live at the points with a test light, I have also checked the ignition switch and there is a live there too
P Thompson

This thread was discussed between 21/04/2011 and 24/04/2011

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