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Hello everyone, my first post here!!

I tried starting my 1972 mgb gt yesterday and had no success. Their was no power at all, even the ignition light didnt come on. This has never hapened before.

Previously (few months ago) i had trouble starting as i think she lost charge in the battery, i put this down to a few months of no use. I got her started off my other car in the end and went for a long run to charge her up. This was fine and started again later on.

My battery and alternator are both a year or so old. I believe its the wiring or bad connection somewhere.

Where do i look and what can i try or do, please bear in mind im thick when it comes to cars and a total beginner.

Im sure if i connect to my other car it will charge up fine and if i use it regular it would work fine.

Hope that helps


Try looking at the Brown wire, under the car, at the starter

In the U.S., this wire is held on by a push-on tab connector
and it sometimes jiggles loose. When this happens everything
goes dead.
Daniel Wong

Worth checking the battery clamps are not high resistance. Turn on the sidelights, if they work then die when you turn the key its worth cleaning the battery terminals, the grease over them, vaseline usually recomended but I find lithium grease keeps the water out and does the job.
Stan Best

I've left my 73 a couple of months before now, on batteries I've had for years, and it started up OK with just a little slower cranking than normal. But if you have an alarm that could well flatten it in 2 or 3 weeks. An old knackered battery with internal shorts will also flatten much quicker than a good battery.

If the ignition warning light didn't even come on before you tried to crank then either the battery did go completely flat which means it must be very bad or there is a drain, or there is an open circuit connection in the battery connections. If you used jump leads on the battery connectors then the only place the open-circuit connections could be is between those connectors and the battery posts. An open-circuit further forward i.e. in a brown wire would stop you jump-starting it as well. Using the jump leads could have joggled the connections and remade any open-circuit, you should make sure this fault doesn't exist before starting and running the engine as you must not do that with a disconnected battery.

You can check for a drain by turning everything off, disconnecting the battery earth strap, and connecting an analogue voltmeter on its 12v scale in place of the earth strap. Cars with a dynamo should show zero on the meter. Cars with an alternator will probably show a few volts, which is the alternator, unplug it to check and it should drop to zero. If you see a full 12v you have a drain, which could be something very small like after-market clock, radio, alarm etc. so these should be disconnected. If you still see 12v remove the purple circuit fuse (bottom one), and if still there you will have to start disconnecting browns from things like the main lighting switch, ignition switch, starter relay and finally the solenoid. If you don't have a meter then you can use a low wattage 12v bulb like from a torch or test-lamp, but this won't show very small drains.
Paul Hunt

Paul's explanation is pretty thorough. I'd clean the battery post connections first. If you want, you can install one of those switches with a knob on the side to one of the posts at the same time. If you're going to leave her still for a month or so, just turn the knob to disconnect any drain. Just one or both of those things might fix you up. Or not.

I've fitted a cut-off switch to both of mine. Originally to the V8 to stop the alarm flattening the battery when I stopped using it as a daily driver, I subsequently fitted one to the roadster as well primarily as a safety feature. I have known electrical gremlins cause things to start happening when the car is parked up (in one case (not my car) cranking it across neighbouring front gardens) and it is also essential if a short should develop on one of the many unfused brown wires. The alternative of stopping the car, getting the tools out, removing the battery cover and undoing the battery ground strap while the wiring is burning merrily doesn't bear thinking about.

For preventing the battery flattening over time *don't* get one with a bypass fuse (for obvious reasons I hope). I did wire from the battery via an in-line fuse to the after-market clock on the V8 as I was fed up resetting the time every time I got in.
Paul Hunt

Right thanks for your help so far guys.

I dont have a voltemeter and hate electricity. lets just say we dont get on and therefore i have respect and stay away from trouble.

I would just like to re-iterate i now nothing much about cars.

If i can offer something else, its that i am using one 12v battery, if that effects anything. Also i went off the round last year into a ditch, luckily i got the car fixed and only thing wrong was earth or something to the back of my dash. As at the time the battery would just die after a few minutes of use and you see the voltmeter go slowly done.

Also yesterday i got her connected to a car and started up okay, so i thought i would take it for a drive to charge the battery. I did about 16 miles, then i stopped and switched off. The only thing that hapended was the ignition light came on, their was a griding noise and only about 8volts and therefore nothing hapended. I got the car charged again off a friend and drove 1 mile home, stopped the car and its dead again.

Does this throw anymore light onto it???

Sorry to be a pain and be stupid, im no mechanic or very good with my hands but i still love the old girl and dont get wound up about these problems, classic cars are fantastic to drive. I believe its her personality!!

Please help

cheers andy
andy walmsley

To be honest, given your 2nd paragraph I don't think we are going to be able to help. There should be enough information already posted for you to come back with the results of the tests so we can move forward, if not fix the problem. Unless you are willing and able to use things like voltmeters or testlamps all we can do is give you a list of things to change in the hope that one of them will do the trick, there is no guarantee of that, and it could be very expensive. It might be a case of "pick the car up by the radiator cap and give everything underneath it a 1/4 turn to the right, discard and replace. Then fit a new radiator cap".

A 12v battery if anything makes things simpler as there are two less connections that could go wrong. Going into a ditch, if it resulted in body damage, could well have jolted the battery badly and caused internal damage. And unless you or someone else has done a proper job of clamping down the 12v battery in the 6v hole then the joggling about in normal use is likely to reduce battery life. And if the battery terminals came into contact with the battery cover when you went in the ditch that would do more damage to it.

It sounds like it might not be charging if you drove for 16 miles then it wouldn't restart, or it could be bad connections as previously mentioned, there simply isn't enough clear information in your posts to tell. You say you don't have a voltmeter but then describe seeing "the voltmeter go slowly done" and give us voltages.

I'm sorely tempted to say take it to someone who knows what they are doing, but unless you know someone who is a whizz with electrics taking it to most garages will cost a lot of time and money.
Paul Hunt

I may have missed something here, but have you tried a new battery? You seem to have a voltmeter as part of your instrumentation and it shows 8 volts. I use a battery on my bench to test fuel pumps and last week it went from a healthy 13 volts to 7 volts overnight and wouldn't charge any more than that. New battery solved my problems.

Tony Oliver

Andy, no need to appologise for lack of knowledge. From the symptoms, I would expect an auto electrician to be able to find your problem rather quickly. As suggest I would buy a new battery from an Auto Electrician and have him instal it, he should run some quick checks to make sure it is charging and when he is instaling he can check for leakage. Don't just buy a replacement battery from K-Mart.
Due to my lack of electrical knowledge I have developed a long team working relationship with my local Auto Electrician, who will even do house calls when my efforts to repair electrical problem only make them worse.
David Levy

This thread was discussed between 18/02/2009 and 25/02/2009

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