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Electrical Problem

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teddymcmur

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My 1980 MGB has always run beautifully, at least for the 6 months I have owned it, however, today without warning while driving it, the radio stopped working, temp and fuel gauge stopped working and the windshield wipers stopped along with who know whatever else I didn't notice. The car continued to run fine until I got home. I turned it off but it would not start again - completely dead; however the clock and interior light continued to work. I hooked up a battery re-charger and it immediately started again. I do not have the equipment, nor the expertise, to check the charging system, but I did check the battery with a cheap store bought tester, and it indicated at least three of the cells are in dire need of re-charging. The battery appears to be very old - it came with the car. Also, while driving home, the aforesaid items which had previously stopped, came on and off again several times. After getting the car started, I drove it around the block several times and the same things stopped working again and shortly after that the car died while I was driving it.. I was able to jump start it to get it back home. Once home, I turned it off and it restarted.

New battery? Alternator. Any thoughts. I'm stumped.

Thanks.

Michael
 
since you say the battery is old, replace it first and see what happens. Technically, it shouldn't matter once the engine is running, since you run on the alternator at that point, but it's worth a shot. I'm not sure how negative ground systems react to bad batteries too, so there may be something that could affect the electrical system if it uses the battery as a voltage reference or something. If a new battery doesn't do it, I'd check for ground faults and shorts(since it's free) and then th alternator. It sounds like an alternator to me.....
 
[ QUOTE ]
, but I did check the battery with a cheap store bought tester, and it indicated at least three of the cells are in dire need of re-charging. The battery appears to be very old - it came with the car.

[/ QUOTE ]


start there.

put a new battery in and check all wiring


mark
 
[ QUOTE ]
and it indicated at least three of the cells are in dire need of re-charging. The battery appears to be very old - it came with the car.

[/ QUOTE ]

Mike,

Go get a new battery. With three dead cells loading down your alternator, I'm surprised it runs at all!!

Rob,
Your almost right. While the car IS running on the alternator while the engine is running...the main task the alternator will be doing is charging the battery and with three dead cells (probably shorted) it will have a beast of a time trying to keep up. On top of that, with an alternator, the battery supplies an excitation voltage to the alternator as there are no permanent magnets in an alternator. The (maybe) 6 volts may not be enough to do this job so that the alternator won't be able to keep up with the needs of the car. A new battery is needed and should fix this problem.

Mike
 
In my experience, a battery that needs just charging will not read that low. Maybe around 11 volts or higher. If it reads 10 v, one cell is completely dead and the battery should be replaced. With three dead cells, it is hopeless. Get another battery definitely. After replaceing it take that volt meter and read across the battery with the car running and you should get somewhere in the vicinity of 13.8 volts. If it reads only right at or a little above 12 volts, troubleshoot the charging system or wiring or connections. But start with the battery and you will save a lot of aggrivation. I am assuming you have one battery. Mine was converted to one 12 volt battery before I bought it 23 years ago. You still should get that same reading across both 6 volt batteries.
Bob
 
[ QUOTE ]

Rob,
Your almost right. While the car IS running on the alternator while the engine is running...the main task the alternator will be doing is charging the battery and with three dead cells (probably shorted) it will have a beast of a time trying to keep up. On top of that, with an alternator, the battery supplies an excitation voltage to the alternator as there are no permanent magnets in an alternator. The (maybe) 6 volts may not be enough to do this job so that the alternator won't be able to keep up with the needs of the car. A new battery is needed and should fix this problem.


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good info mike, that makes sense. For some reason I was assuming failure of the battery to an open circuit condition, if it's short that makes a lot of sense..... /ubbthreads/images/graemlins/thumbsup.gif
 
Before you do any of the more expensive cures, I would recomend that you check the ground wire to the battery to make sure it is tight...what you have discribed is very reminisent of a bad ground wire on a batery. Could be as simple as tighening it /ubbthreads/images/graemlins/grin.gif

Bruce /ubbthreads/images/graemlins/driving.gif
 
Well, checked on everyone's suggestions today and only found a disconnected iginition warning light at the alternator, which is why the ignition warning light never worked. It glowed bright red once I connected it. Of interest, connecting it also fixed my turn signals which were not working consistently. Had a great conversation with John from University Motors and he walked me through everything and with the aid of a friend who had the right equipment, the culprit appears to be the alternator. Hopefully, a rebuilt one will be installed tomorrow just in time for this weekend. Thanks to everyone for your suggestion. It was all very interesting and helpful.
 
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...at least three of the cells are in dire need of re-charging...the culprit appears to be the alternator...

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Likely you will still need to replace the battery. If by "dire need" you mean they were below 10V, not many batteries can go there and come back.
 
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I do not have the equipment, nor the expertise, to check the charging system. . .

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Michael, I beg to differ.

Your post indicates that you're in Sarasota, Florida. Quick websearch indicates an Autozone parts store at 3251 17th St, Sarasota. phone number 941-954-2234.

I can only imagine that Autozone's policy is the same at all locations, and if that's the case, they'll test your alternator and battery for free. All you have to do is get the car to their store and one of the employees will wheel the tester out to the car. Locally they use a fairly nice, computerized tester that is user independant, so you don't have to worry about being misled.

Good luck with the fix,

Mike /ubbthreads/images/graemlins/patriot.gif
 
[ QUOTE ]
Well, checked on everyone's suggestions today and only found a disconnected iginition warning light at the alternator, which is why the ignition warning light never worked. It glowed bright red once I connected it. Of interest, connecting it also fixed my turn signals which were not working consistently. <<SNIP>>.

[/ QUOTE ]

I was about to say it’s your Alternator. Sounds like one (or more) of the diodes in the rectifier bridge is shorted out.

Let us know how the rebuilt unit works out for you. But alas I suspect that something else is going on with the turn signals.

My advice: Can't add much as it seems you've got a handle on the issue. But is if you don’t do anything else, make sure you get yourself a Moss Catalog. They have a great troubleshooting guide in there. Next get a good wiring diagram for you car – you could get a manual or down load one on line. Then I’d go down to the local Radio Shack (or wherever) and get a cheap milt-meter ($15 to $20). This will allow you to perform some of the basic voltage & current measurements, as well as continuity checks of your wiring. Great tool for any tool box.

/ubbthreads/images/graemlins/cheers.gif
 
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