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MG Midget and Sprite Technical - Alternator gone?

Carb trouble solved - next problem arising. The car wouldn't start and it showed signs of a drained battery. I charged the battery and it fired up fine.

I then checked the voltage across battery terminals with the engine turned off and got 15.8 Volts. With the engine running, I got 15.8 Volts as well. I get the same when I disconnect the alternator entirely. Hence, I have a funny feeling that the alternator is not charging at all as there is no explanation why the battery should be drained right after a 15 mile drive. Ignition light was off.

However, I also noticed that the ignition light was not on when it should be (ignition on, engine off). I followed these instructions and the ignition light lit up when the brown/yellow wire was connected to ground. So the light itself is working.

Before I buy a new alternator, are there any ideas what else I should check?

Apologies for the lengthy posting.

A Damm

I'm playing catch up here, see your other thread for more on carbs

I also put there
>>put up another thread about your alternature or look in Archives or recent threads as there may be help for your alternator too<<

IF you should need a new alternator you can get 65 amps upgrades for reasonable money (see my links on other recent-ish thread)

do you really mean you got 15.8 volts??
Nigel Atkins

Yep, I did get 15.8 Volts. But this was from a battery that came straight from the charger.
A Damm

15.8, battery must still be bubbling and buzzing, wouldn't that be above what an alternator can do anyway

try again tomorrow and see what you get

or if you're lucky FRM or someone else that knows might be along before then
Nigel Atkins

True, my idea was to keep the headlights on for a while until I get a lower reading (around 12 Volts) and then start the car. If the alternator is working, I should get around 14 volts. If not, it will stay at 12.
A Damm

Fully charged battery not just off the charger is about 12.6-12.8. You have overcharged the Batt if it stays at 15+ for more than a few minutes - too much of that will kill the Batt.

Alt should be showing about 14.2 hot with a fully charged battery and everything ON at 2000rpm. 13.8 to 14.6 is acceptable, otherwise there is some fault, which should be attended to. Even 13.8 is a sign of something not quite.

FR Millmore

Just a little more info needed

Do you have an alt or is it a generator

Do you have the old mechanical regulator, if its the old regulator, it may need adjustment and contacts cleaned with a glass pen

What year midget do you have
Prop and the Blackhole Midget

What is the thread TITLE?

FR Millmore

Update - I just checked my battery and I got 15.8 Volts (and yes, I know that this is too high). Turned the lights on and checked voltage - stayed high for a couple of minutes but then plummeted to 7.6 Volts. With lights turned off it went up to 12.2 but wouldn't deliver enough power to even crank the engine. By the way, I only charged for an hour or so yesterday to check whether I had a supply or a wiring problem. So, that's a failed battery.To be fair, this is the old battery from my wife's car, but I thought it might do the trick in the Midget - I was wrong.

Re ignition light - can a dodgy battery cause the symptoms I described above (not lighting up when it should)? Or do I possibly have multiple issues of a failed battery and internal alternator regulator (I don't have a dynamo + external regulator)?

A Damm

sounds like you might have used some industrial type quick charger that wouldn't do a standard car battery any favours

and/or you need to confirm your meter is reading accurately - always test the test equipment using it

ignition bulb out could be faulty alternator, or part of, or even wiring or connector(s) to bulb

on any car but especially a classic always have a good battery, in good condition and your battery terminals, clamps and leads clean, secure and fully protected

also make sure all wires, connectors and earths are clean, secure and fully protected

a poor battery wont help with solving electrical problems and often will make matters worse and more difficult to resolve

by the sound of your battery the ignition light should have glowed white let alone red

your alternator and ignition bulb problem might (only might) just be the connector plug or connectors dirty, of the three wires from the alternator plug (big and smaller brown wires) the third double coloured wire goes to the ignition bulb

always best to fully disconect the battery before messing with the thick wires or connectors, just in case
Nigel Atkins


I was just wanting to verify that it was an alt and not a gen. Think back, we have already seen that dog and phony show...but i havr no doulbt after reading some of the thread that this is an ALT.

Prop and the Blackhole Midget

Easy enough to get the battery checked for free, at battery sellers.

It is very possible that the bad battery caused the alt problem, or t'other way round - a mutual death orgy.

Also quite possible that loose or very bad connections killed both.

Email me, ask for "Electrobabble" if you really want to figure out & fix.

FR Millmore

Well, this is embarassing - The battery in my voltmeter was low. Hence the high reading on the car battery. New battery in voltmeter and load charge across the battery terminals checked. Voltage stayed at around 12 volts so nothing from the alternator. Wiring seems ok. Will be away for three weeks and order new uprated alt upon my return. Any recommendations?

A Damm

I seem to recall a company in the states that made an uprated lucas alt.. but i cant remeber who... You might check with an alt / starter rebuild shop about making yours into an uprated would certianly.make reassembly much easier

if your going a differant modern alt ... Then id go with a built in eletronic regulator and a single wire hook up...

Prop and the Blackhole Midget

testing equipment not accurate is a lot more common than you might think hence me putting test the test equipment, you should do this before every test really to be certain

loads of new uprated alternators to chose from

just check that you buy one with the correct socket and that it's not upside down if your wires are short and keep any space parts, the new alt I got had the plug upside down and needed three washers to get it exactly lined up with the fanbelt - one example 65 amps -
Nigel Atkins

Why would an upside down alt be bad... As long as the pulley is being driven in the correct direction
Prop and the Blackhole Midget

I should have been clearer

>>one with the correct socket and that (the socket is) not upside down if your wires are short (as the wires might not reach)<<
Nigel Atkins


Simple solution... Lucas spray on liquid wire streatcher
Prop and the Blackhole Midget

if the alternator is fitted upside down is a roll bar also required?

no don't answer, it was just a thought in my head
Nigel Atkins

A. Damm,
...for when you are back. Check that your Alt. has voltage on the thin wire permanent live feed, else it won't charge. It could still just be a matter of a broken or damaged connector.
Guy W

This thread was discussed between 27/08/2012 and 03/09/2012

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