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MG MGF Technical - Battery?

Having a problem getting the car started.
When I turn the key all I get is a 'buzzing' noise,like a relay or something playing up.
But soon as I put jump leads on the car it starts first turn of the key.
The battery is less that 12 months old,and when I have put a meter across the terminals it is showing over 12 volts.
I have put the meter across the terminals when the engine is running and it shows 13.85 volts.
I jumped the car off this morning and took it for a 40 mile journey,when I got home I turned the engine off,tried to re-start it and all I got was the buzzing noise,(the meter showed 12.82 volts in the battery at this point)
Any suggestions as to the cause of this?

R Appleton

You could try shecking the earth strap where it bolts to the body. Both surfaces must be corrosion free and bolted securely.
Mike Clements

Mike's idea's a good un. I had problems with a new battery recently, it was fine for a month or two then went the same way as the one I took out (not charging after a decent run, failing after a few turns of the engine etc). Borrowed a charger and charged up the battery, reconnected and not had a problem since. I figure the problem was a connection with the wiring.

Helpfully (or not) I didn't check the voltage at the battery terminals after fitting the battery the 1st time. Checked second time and voltage at the terminals and connectors was the same (14 something IIRC). Anyway, figure the battery charger proved the battery was fine. Make sure the cables are connected cleanly and as Mike says, check the other end of the earth strap, it's been known to corrode badly.

Don't forget the engine earth strap!

Tonight is the first time I have had the chance to look at the car since saturday, and the same old problem is there,won't turn over just the buzzing noise!
Checked the battery and it only had 9 volts.
Put jump leads on and it started first turn of the key.
I went for a nice long drive, came back,turned the engine off, checked the battery it had 12.42 volts, turned the key and all I got was the buzzing noise.

I have checked the battery terminals and they are all tight and clean, as is the earth strap to the body.

I found the noise to be coming from the starter motor.

Could there be an earth fault on the starter motor and if there is, why does it work when I put jump leads on?

Poxy car is doing my head in...every time the sun comes out,there is something wrong with it,and when I mend any faults it starts raining!!!

Wish I had bought a bicycle instead :0(


R Appleton

It sounds like a combination Bob. If the battery voltage in a relatively new unit is at 9v, it is either defective(unlikely), knackered (more so) and the probable culprit is a current drain from something not switching off when you turn the ignition off.
Have you checked the continuity of the engine earth strap and also the starter motor +ve terminal?

Check that the integral mirror lights are off. it is possible to move one to the on position when adjusting the mirror.

Also, someone recently suggested placing your mobile phone set in video mode in the boot and closing the boot, also in the bonnet. It just might be possible that a lamp is staying on which would account for the battery drain.

Tony Harrison


If you've checked all the earth points for clean and tight, then I'd get the alternator checked out by an auto-electician.

You've said the battery appears to be charging - 'cos you see 13.75v across the battery when the engine is running. So the alternator must have it's drive belt attached (do check it for tension). But with engine off you get 12v or less, so clearly the charge is not not that powerful as battery is not holding charge - or is being drained to earth straight away.

Could be the alternator diodes are breaking down and doing reverse drain to earth when off and do not deliver enough power when charging.

Batteries are measured in ampHr i.e. the amount of hours at 1 amp draw that they can deliver 12volts. Power(Watts) = Volts x Amps. It sounds like you don't get enough Amps through the charging circuit to keep the Power up. When the starter draws Power, there's not enough in the battery, hence the not enough power complaint ("buzzing") of starter-relay or starter motor.


J Lennon

Yeah the car is working again...It was the battery, I took it back to the shop, and they tested it and said it was 'cream crackered'

I put the new one on the car and it starts first time every time....Still haven't managed a drive with the roof down as it seems to be raining a lot just lately

But I live in hope !
R Appleton

i cant help but laugh at this thread, i mean the way he put it i mean with the bike... i havent laughed like that in a long time... but yea i know wot ya mean.. i have the same luck mate...

I to have recently bought an MGF 2001 model this to has a problem where the car will start ok and drive for may be 4 hours then the abs light and battery light will come on the dash the and eventually the car will stop driving. could this be alternator?? the positive lead on the battery was rusty but now cleaned to polished barss.


Ken, your problem certainly sounds like a failure to charge, and the alternator certainly requires checking. Check the voltage over the battery at ingition off, ignition on and tick over. Should be around 13, 12 and 14 volts respectively assuming a good condition and well charged battery (see other contributions above). If the voltage across the battery falls below 12 volts with the engine idling, then I would presume that there is a problem with the charging circuit - whether that means a problem with the connection, the loom (wire break?) or fundamental problem with the alternator itself.

Good luck, and let us know what the problem was!
Rob Bell

This thread was discussed between 20/06/2009 and 23/08/2009

MG MGF Technical index

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