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MG Midget and Sprite Technical - '73 RWA MKIII - Running out of electricity...


Just taken a day to get from Bedford to Oxford via Sherington.

I saw a couple of MKIIIs on my way back (hello again if that was you).

Right, scene set:

I've left my midget for long periods before (3+ weeks) and when turning her over after a sit she spins over fine and starts after only a few turns.

I landed in Bedford Saturday afternoon after a lovely sunny drive from Oxford, 26 degrees and she didn't overheat, was behaving fantastically. When I pulled up outside my parent's house I heard some burbling and noticed she'd dropped some coolant after I stopped. Thought is was odd and topped up this morning.

Came back from church and had some lovely roast lamb (totally unrelated to the Midget issue, but still necessary information).

Went and set off to Sherington (MK) to visit a friend. Car had obviously only been sat over night. Wouldn't start. Battery flat.

Checked for anything shorting or anything electrical left on, couldn't seen anything. Jumped off my father's Previa and headed on my way. Everything was fine to MK. Had a cup of tea with my friend and took him for a drive after having to jump again. The exhaust fell off (separate issue (it's been a long day)).

Luckily I had a spare rubber mount so we fixed it in 15 mins with fresh bolts.

I headed from his and got as far (with no issue) as Tingewick bypass and she started missfiring and spluttering.

Initial thought was of course fuel. I had over half a tank and I know my empty is just past quarter.

I tip-toed her to the end of the bypass in the direction of Bicester where she spluttered more and more and finally conked past those lovely thatched cottages on the left (if you know the area).

I was offered a cup of tea from the owners for which I am very grateful.

The fuel pump was still working and dragging through lots of fuel, so I had to rule out fuel. The battery was to flat to attempt to turn the car over again. the lights wouldn't really work either.

I got my friend I had just left to come out with lead and a jerry can regardless.

We linked up his 9000 to the Midget and it was reading 11v, when usually it reads 14v running. Obviously 3v was being drained to me.

It was obviously running fine so we D/Ced the leads and watched as he lights got dimmer and dimmer...

My only thoughts to the problem is alternator rather than battery.

Any other ideas? How does one test if it's the alternator that's packed up or just the wiring connecting it?

Apologies for the long thread and thank you if you've made it this far...

Any help gratefully received.

- Richard
R L J Oakley

If you're getting less than 13V across the battery when the engine's at fast idle, your alternator is probably caput.

This assumes no other problems, e.g. the alternator is connected to solenoid; good connections to battery etc.

First check the plug in the back of the alternator is securely in place... oh, and the fan-belt is working...(!)

Anthony Cutler

what Anthony said, plus one more thing: make sure the indicator light on the instrument panel lights up when you turn the key. If not, it is probably burned out or disconnected. Because it is in the exciter circuit of the Alternator, that light bulb, burned out, turns "off" the alternator.

Norm Kerr

Assuming your car has one of the PITA Lucas alternator connector, 2 large spades for power and a small one for the ignition light, I'd check that they are clean as they have a habit of oxidising and overheating in my experience which produces electrical issues similar to what you describe. Also depending on how it has been wired I'd check that the 2 large power connectors are commoned. I had a Caterham that was wired so the alternator common was connecting the battery to the loom and that common started to fail causing problems as you describe, especially with the ignition as the loom power was becoming intermittent.
David Billington

The indicators work is the car's connected to another car. Everything goes rather dim if running by itself.

I have two large connectors next to each other on the back at the top and then a smaller one underneath. Only the top large spade connector and bottom small spade are connected. The middle one isn't I found a taped up wire with a large spade end just loose ion the engine bay. I connected that but it made no difference.

The battery was reading 6v when running by itself.

- Richard
R L J Oakley

just notes

photos might help about the thick brown wires/connections

clean up the alternator plug connections as if all the new alternator plug kits with the spade connectors are the quality of the one I bought then stick with the original if you can

I think Norm is talking about the ignition light abd you may be thinking of the side indicators??? but I could be wrong

what ever else happens keep your battery topped up with distilled water in each cell and battery fully charged or it will hinder rather than help, if the battery gets suspect then change for new as a good battery will help with electrical problems

IF you have to change the alternator consider an uprated version

and of course don't leave the car 3+ weeks without driving it - or you'll get electrical problems :)
Nigel Atkins

Mike Howlett put this up on another thread, it might be of help here -
Nigel Atkins

The car has been fine for 5 months are being left, as I said started first time. I sometimes find it hard to drive cars when you're not in the same county as them.

I'll keep on top of the battery, but surely this it alternator woes?

I was thinking of the indicator lights on the dash, I thought that's what he said.

I'll get some photos up asap

- Richard
R L J Oakley

The 2 large connections on the back of the alternator connect to the same point believe it or not so would not make any difference when the second wire is re connected. They do both need connecting however as you need to split the load between then so that you do not over load one wire.

Your Alternator is Kaput and the spluttering was the result of lack of electrical power to power the ignition circuit.

Go to you local Auto electricalfactors and let then either supply you with a new alternator or repair your old one with possibly a diode pack complete with new brushes.
Robert (Bob) Midget Turbo


In the case of the Caterham I had for safe keeping for a bit one terminal was connected to the battery and the other to the loom so the common in the alternator was part of the circuit and when it started to fail it really caused issues with the electrics. I cleaned them up and commoned the terminals and sorted the alternator. I wouldn't have done it as it had been done as I don't think the large spades stand up that that well at the sort of currents they might have to pass in that configuration.
David Billington

Richard the last comment was meant to have humerous wording

if you're out of the country yeap it'll be difficult for you to drive the car, perhaps I could help out with the driving ... narh, I thought not

What I meant with keeping the battery in good condition not just for this fault but for future problem solving so that the battery by having plenty of power don't stop the investigation and repair process on other electrical faults in the future and of cousre easy starting and running equipment

During days like now the car will run for quite a while on good battery power only so disguise the alternator problem for a while - I know I would have completeled a weekend tour of Belguim if I hadn't forgot to turn my headlights off after a couple of 'mountain' mist doh! lead me on to a very expensive alternator replacement "situation"
Nigel Atkins

Apologies for not picking up the tone.

I have been tempted to invest in a battery charger. Seen second hand units on the 'Bay for not too much.

No wiring's changed or been disturbed from what I can see, how much longer should I be playing around with wiring until I bite the bullet and buy a new alternator?

Any further checks I can do with a multimeter on the alternator itself? Anything that would show up a fault unit even if I've connected the battery to another car?

- Richard

R L J Oakley

Hey my posts are never the best written

Borrow a battery charger (I can't remember the last time I used mine on my car but a couple of neighbours were glad of it this winter)

If you have mains power available the battery conditioners are very good for car storeage

Others will be along with how to test the alternator (if it's not in that link I posted earlier, press up arrow for top of page)

As I earlier said IF you have to replace the alternator consider upgrading not much more money you can get recon ones or s/h if you don't want to pay full for new

I've got an upgraded alternator on the battery that came with the car 4 years ago and an electric fan that I've wired directly to the battery (with it's own fuse) so everytime I stop the car the heat rises and the fan cuts in draining the battery - no problem
Nigel Atkins

This thread was discussed between 24/04/2011 and 25/04/2011

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