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MG Midget and Sprite Technical - Generator light on

Driving home from work tonight, I used the wipers to clear the screen. They jammed about halfway through the stroke, but after a second they freed and parked.

But the generator light came on and stayed on!

I nursed the car home on sidelights (60 miles, mostly unlit motorway!).

What can have caused this? I haven't popped a fuse and the battery seemed to have lots of life in it, although the headlights don't brighten when I rev the engine (not sure if it used to do this before the red light appeared!), the car runs fine and starts as always, engine spins over at normal cranking speed.

It's a 1275 Sprite with a Neg Earth Generator.

Thanks

Andy
a borris

Could be the alternator. Best check the voltage its giving out next time you start the car.
Brad (Sprite IV 1380)

Thanks Brad, where's the best place to take a reading? At the control box or at the generator?

Andy
a borris

or the fan belt,to test select dc volts, read across the battery and take a reading with engine off, should be about 12.7 volts, start the engine and volt reading should be 13.5 to 14.5 volts, if no volt gain then replace the alternator after first checking the wiring is in good order.
Alex Sturgeon

Thanks, just need to point out it's a generator with control box.
Twice as much to go wrong?

Andy
a borris

look at the brushes in the gen, and the contact tips in the control box, if not replace with an alternator, simply job and removes two problems
Alex Sturgeon

You might try Paul Hunt's Pages of Bee and Vee. The spanners section has very good diagnostics of the charging systems. http://www.mgb-stuff.org.uk/
David "no generators" Lieb
David Lieb

Andy first thing check the voltage across your battery with the engine running . Should be more than 13 volts, about 14 to 14.5

I am sure it will not be because otherwise the ignition lamp would not be on, anyway needs checking first.

Because this happened when the wipers stuck on, then it could be that you overloaded a circuit. Hopefully this might mean that the 2 wires at the back of the dynamo are simply loose and you now have poor connections, these need checking at the dynamo and at the control box/voltage regulator

If than is not the problem then you must check the dynamo in the following manner

Disconnect both cables from the connections at the back of the dynamo and with a short piece of wire connect both terminals (D and F) together. Then connect the negative lead of your meter (set to measure at least 30 Volts DC) to the short piece of wire and the positive lead of the meter to a convenient earth on the engine/ car body.
Start the engine, let it tick over and measure the voltage. It should read about 15 to 20 volts depending on the speed at idle. Revving the engine slightly should give a figure of about 30 volts of more.

If the dynamo is faulty then check the brushes if not then test the voltage regulator/ control box

On our website you can view the original lucas manual that will help if you can't sort it with normal info
try here and check LUCAS TEXT http://www.mgcars.org.uk/mgcc/midgetreg/chargingsystem.shtml

Bob (Robert) Midget Turbo

This thread was discussed between 19/12/2008 and 20/12/2008

MG Midget and Sprite Technical index

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