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MG MGB Technical - arrgh - no battery charge again!!

Help needed - again!!

Fitted hazards to my 72 car two weekends ago. I followed the wiring diagram from the haynes manual for "later" cars. I took the brown to power the hazard flasher unit off of the back of the ignition key switch by cutting wire at terminal, adding in second wire on new connector and running to terminal on flasher unit.

Few days later i turned the car over on the key, but no charge in battery. Fair enough i thought - fitting the hazards took about four hours and courtesy light was on all that time so, possibly ran it flat in that time... There was power there, but it was having trouble turning the engine over.

Anyway jump started it and got it going.

This saturday i needed to work on car again and so got, in and tried to fire it up - flat battery again!!> This time also enought power just to turn it over, but not really to start it.

When i got it going (another jump start) i took it for a good 30 mile blast after letting it warm up lots before taking leads off etc.

I did the work this time by taking out bulb to courtesy light so as not to attack battery.

Sunday i finished off work on car - tried to start it, fine.

Today, not even enough charge to light up the courtesy light (yes i did put bulb back in!!), nothing on the key when trying to start, not even click on starter, no power to turn on wipers etc - really flat!!

So - have my batteries just bitten the dust, or has it got something to do with where i have taken the power for the hazards from???

Surely the brown circuit is the same where ever it is taken from?? I didnt have this problem by taking the power for my headlamp relays off of starter relay so why should the brown off the starter key switch be any different?? I would have thought that as long as hazards are off there is no charge being used??

Assistance apreciated as ever...

~PHIL

Phil

Phil. A "quick check" of the battery (or batteries) is to charge them fully, leave them in the car, but disconnected from the system and let the car set overnight. Reconnect the battery and see if they are flat. If they are, bad battery/batteries. If they are good, they should start the car. Do not know what could be the problem with the flashers. Here in the US, we had them from about 68 on, perhaps even earlier. Thus, I would thing that rather than use some "generic" wiring diagram, obtaining one for the US version of your year would be better. Certainly removing the brown wire you installed, after proving the batteries good, should allow you to determine if it is a problem with that circuit. Paul H should have more and better ideas. Les
Les Bengtson

If disconnecting the batteries overnight allows them to retain their charge as Les suggests then you do have a drain. Remove the battery ground strap and replace it with a voltmeter. If it shows 12v then you do have a drain. If you only see 5 or 6 volts or so that is the reverse leakage of the alternator diodes and is quite normal, you can unplug the alt to check if you wish.

But if you do see 12v then unplugging the alt is the first step. If the volts drops to zero one or more of the diodes in the alt is leaking more than it should. You used to be able to replace just the diode pack.

If no change remove the bottom fuse in the fusebox (brown to purple). If the voltage goes there is a drain on the purple circuit which feeds things like interior and boot lights, horns etc.

If no change you will have to start disconnecting browns. These start at the solenoid and go to the fusebox, starter relay, ignition switch, main lighting switch, and in your case the hazards which should be via an in-line fuse.

Which ever one causes the voltage to drop to zero is the one that is feeding the drain. If you can only get rid of the drain by disconnecting the browns from the solenoid then the browns themselves would appear to be shorting to ground somewhere. If removing the browns *still* shows the drain the leak is either inside the solenoid or on the main battery cable.

Note that dampness on the top of batteries with exposed cell links can also show up as small drains on the voltmeter.
Paul Hunt

It appears that the RHS battery (driver side in UK) is faulty and i have monitored it losing charge throughout the day - there being no charge this morning after charging on wednesday.

Charging system fine, showing over 14 volts on fast idle.

THanks for the help guys, invaluable for future refernece.

I shall probably take this oppurtunity to change the BGT to one single 12v battery. Can anyone tell me the Cold Cranking Amp (CCA) rating required, will 360A be sufficient, or better to go for 500A ???

Have been down to halfords today and looked about for suitably sized units, found both as rated above and not sure which to go for.

Paul - where you say to remove the earth strap and replace with voltmeter, do you mean to bridge the voltmeter between the earth pin on battery (where strap removed from) and the earth point on body???

Thanks

~PHIL


Phil

Ive got the same problem. I appear to have a duff cell in my RH battery. Where is the best place to get a new 6v battery from and how much are they ?. MGOC are listing them at £40 each which sounds a bit steep to me. Even better does anyone in my locallity have a second hand one they are willing to part with cheap (but good).
Paul Hollingworth

Phil. Cold Cranking Amps is of little concern with an MGB. Most batteries, made today, have sufficient capacity. The old advise was to have one CCA per cubic inch of engine displacement. I used a 350 CCA battery in a 289 Mustang and a 500 CCA battery in a 427 Corvette when living in Wyoming and parking the cars outside. They always started.

The way I bridge the battery to earth is to connect one probe to the battery "pin" or "post" and the other probe to the battery clamp. If the condition of the battery cable or its connection to the frame is in question, connecting the second probe to the body will show that problem. I picked up a couple of large spring connectors, as you have on a battery charger, from Radio Shack, along with a couple of "alligator clips", or small spring connectors. Attached one of each to a short length of wire, one red and one black. Connect the big ends to the battery and ground cable, the small ends to the probes. Gives me hands free operation. Just make sure you keep the probes apart and insulated. Les
Les Bengtson

I have always found that the surest and very cheapest way to check whether a battery is finished is to use a hydrometer. You can get a tiny one from a car spares shop which can be kept in a cigar tube in the boot or a larger one which is easier to read. Price should be less than £10.00. It tells you whether the battery is OK and which cell is the dud - not that helps as I don't think that it is possible to fix a dud cell.
Marc

Les

Thanks for that - although i can never remember how to convert cubic inches to cubic centimetres (we're semi metric over here ;-> ) I do know that a mustang is of greater engine capacity than my BGT so it take that a 360CCA battery will suffice!!

Paul Hollingworth

If you are looking only to replace your duff batttery and are willing to pay postage you can have my other 6volt battery.

I will be changing to one 12v this weekend and therefore it will be of no use to me. I have just checked the batteries again and can assure you that it one of them is holding charge correctly.

In actual fact, I may be passing through hereford next weekend on my way south, so if you want it then we can possibly meet then if you can wait that long - let me know.

~PHIL

PS - I inherited a hydrometer out of my late gradnfathers numerous tools, i'm pretty sure my mother may have just thrown it out after clearing the shed out, dagnammit!! A sure fire thing that you need something only after its been got rid of.... :-<

Phil

Just a note: on this side of the Atlantic most modern batteries are maintenance-proof, so a hydrometer is of little use.
George B.

Phil - yes, or to the ground strap battery clamp. But this test only reveals leakage, not poor connections. For that the system must be connected up as normal i.e. ground strap on battery, and you use the meter to measure the volt-drops between the battery posts and the solenoid/motor during cranking. Ideally you will only see about 0.25v per 'side', if you see more than 1v it is worth testing in various places along the heavy current circuit to isolate where the bad connection (or connections) is, not forgetting the interconnecting cable on twin-6v systems.
Paul Hunt

Paul - sorry for this, but theres yet more.....

I started to notice a tail off in volt drop in the suspected faulty battery yesterday, after my last post. Previously i had the positive side connected and whilst fiddling was noticing the drop. After i isolated the battery completely however, this voltage drop seemed to slow and it now appears that the battery is roughly constant in voltage around 4.15v making me suspect i still had a leak.

SO to make sure i wasnt imagining things, i went out and played again this morning, retracing my steps. Upon bridging the voltmeter at the earth clamp i read 4.15volts (the power left on the RHS battery, the earth side battery, or LHS battery - which ever you prefer - is disconnected).

This goes back to your original diagnosis.

I have removed the brown at the starter solenoid, the starter solenoid relay, the back of the headlight switch, the ignition and the hazard connection (which i made off of the ignition brown). None of these show a drop in volts. With all of these removed i am still reading 4.15v when bridging from negative batt terminal to earth point (Am using the earth strap where it connects to the body)

So according to your first post, this indicates either solenoid or battery cable. I have had a quick look under the car to check for immediate breaks or scrapes in the cable and cant find any(this obviously does not highlight internal breaks) - is there any way of checking the solenoid for correct function??

Cheers for your help so far!!

~PHIL
Phil

Phil - 4.5v is the sort of leakage I have seen from *good* diodes in an alternator and has caused me no problems. But if you see tha with the alt disconnected then it is worth following up.

If you take the battery cable off the solenoid as well as the browns, and the meter shows 0v, then the problem is either a conductive surface on the outside of the solenoid or partial breakdown of the insulation inside.

If that doesn't do it take the battery cable (that leads to the front of the car) off the battery. If it goes now the problem is in the battery cable insulation.

If it *still* doesn't go, call for Mulder and Scully! But as I mentioned earlier, batteries with exposed cell links that are clamped into the battery boxes can get minor leakage from surface dampness.

Paul.
Paul Hunt

This thread was discussed between 20/11/2002 and 24/11/2002

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