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MG TD TF 1500 - Battery dead, won't start?

The igniation light stays on when the car is runing. It goes out,almost, when the RPM's drop low. I think it is working backwards. I have put almost 360 miles on the car and it started with out any trouble for the past 3 weeks. Took it on a 188 mile trip to the hills and back, ran like a top. Drove it today at 5:00pm to the store, got back in to return home and it worked great, parked the car in the garage and about 8:00pm went to go for a ride and it was dead as a door nail. No lights, no horn, nothing, just dead. It is like something just drained all the energy out of the battery. I am charging it on slow charge and will see if it starts in the morning. What is wrong? I do not understand my problem. I did all the tests you guys recommended, the volts seem to be correct, etc. I need help. I know I have asked about this before, and I don't mean to be a pest, but I am lost .Attached is a picture of my car, not perfect but a fun driver.
Thanks;
Louis

Louis Levin

If it weren’t for the ignition light staying on, I would say check the battery cables particularly the ground at the body.
David Werblow

Louis,

Does the ammeter indicate a charge?

Batteries can fail to take a charge, or keep a charge. After you charge the battery, measure the voltage across the terminals. It should be above 12.5 Volts. After a long drive, measure the voltage again, it should still be above 12.5 Volts. If not, either the generator isn't charging the battery or the battery won't take the charge. The next morning, same result, 12.5 Volts. If not, the battery won't keep the charge, or there is a short somewhere. Disconnect the ground at the battery. You can put a DVM on the ammeter setting between the ground and the battery, and with the setting on current, should read zero with everything off. If not, look for shorts by disconnecting one wire at a time by the fuse box. That will isolate half the car. From there it is finding a culprit.

According to Lucus:

"One side of the ignition warning light should be connected to the output side of the ignition switch and the other side to the D terminal at the control box. With the ignition on and the engine off, the battery voltage is applied to one side of the warning light from the ignition switch. The other side is connected to ground by the generator armature and brushes. When the engine is started and the RPM increased voltage from the D terminal rises at one side of the bulb to oppose battery voltage at the other side. The warning light fades until both voltages are equal, and the light goes out. At almost the same instance the cut-out points close (at 13 Volts) thus shorting out the warning light and allowing the bulb to stay off.

"A warning light will glow faintly when there is internal high resistance in the ignition switch., Dirty control box cut-out contacts, a slipping fan belt" (do not overtighten, they work with even an inch of slack, and you want that much to preserve the bearings in the water pump and generator DAB)

The ignition warning light will not always tell you that you the charging system is operating properly.

You can test and see if the ignition light is wired right by disconnecting it and then putting a test bulb between A1 and D on the regulator and seeing if it acts correctly or the same as the one in your car.

I hope this helps,
dave
Dave Braun

Dave; thanks for your input. Now the big problem. I charge the battery and went to connect the ground to the battery and big sparks. It appears that the reason the battery was dead is that there is a short somewhere. Oh, by the way the battery does show 12 volts.
How do I find our what happened, other words check for the short? I am a real novice when it comes to this sort of stuff, so I am just at a loss.
Wish there was someone in my town who knew what to do with an MG TD.
Louis
Modesto, CA
Louis Levin

Have to find the short by process of elimination. I would rig up something to make contact away from the car (with a circuit breaker or something in the line?)- maybe even "extend" the battery to cable connection with jumper cables or a long heavy wire- sparks next to a hydrogen producing battery and possible gas fumes not a good idea. One suspect would be a bad regulator (with stuck cut-out), since you have been having charging issues. Try removing the generator wires one at a time first. Then the big cable to the starter (to make sure starter swtich isn't stuck/shorted).Then the fuses one at a time- although it seems they should blow if that big a short. Then you are down to the unfused things- all of the lighting etc. Of course do a good visual for chaffed wire, or a loose or burned wire behind the dash. Hope this makes sense. If you think this is over your head, may be better to find a club member or an old-school sports car shop that could figure it out- you don't want to burn the car up. George
George Butz

George: Thank you. I checked the generator wires, OK and then disconnected the starter, and found out that was what caused the short. Now what do I do? The cable to the starter is disconnected, the lights work, the fuel pump pumps,etc. What is wrong?
Louis
Louis Levin

Louis,
is it correct that every thing works as long as the starter is dissconnected???? And no sparks???

SPW
Steve Wincze

Louis,

Good work. Two bolts hold the starter on, along with the bracket for the return spring to the gas pedal. So easy to take off. You can get the starter rebuilt, or you can track down an early MG midget starter and change the connections. I'm assuming someone hasn't converted you to a starter with a solenoid, which bypasses the pull switch on the dash.

But the starter should be isolated from the battery unless you are pulling on the pull cable which closes the start switch. That's the switch on the RH side of the firewall (as from the driver's seat) that the battery cable goes to and on the second terminal the cable goes from there to the starter. So it sounds like the failure could be in that switch. They are available on EBAY.

You should be able to disconnect both cables from the switch and see if it will connect current and disconnect current. You could use a digital voltmeter set on ohms, or you could simply leave the battery hooked up and disconnect the cable that goes from the switch to the starter. In its place put a 12 volt light bulb, and from there a wire to ground. If the bulb goes on and off as you work the switch, it is probably good.

I hope this helps,
dave
Dave Braun

Well it is working. I checked out all the things you recommended. I checked out the starter switch,etc. Yes Steve everything worked with no sparks when the starter cable was removed. I now have everything hooked back up and the battery does not spark when I hook up the positive earth. By the way the starter is an Lucas stater and was rebuilt about 6 months ago.
Something must have been stuck in the starter switch to draw all the power out of the battery. It took about 36 hours to recharge. I disconneted the battery when I charged it.
I feel better now that it working. These cars keep you on your toes all the time.
Thanks, everyone for your ideas and help.
Louis
Louis Levin

And, it has to be a confidence booster to have solved the problem in your own garage. Congratulations! But keep an eye on the switch, and if you get strange charging indications on a drive, suspect a stuck switch or an engaged starter, and troubleshoot as you did for this. At the very least you could disconnect the cable going to the starter at the switch, and continue on.

warmly,
dave
Dave Braun

Any chance a stray wire or wire strands at the starter terminals caused the problem? If so, don't read on!

Assuming the starter was rebuilt properly, it does appear that the switch was the problem. My preference would be to replace the switch as soon as possible. The switch conducts a huge amount of current. If it shorts to the starter motor, your starter will run continuously until the battery runs down. If the engine is running, too, you could do damage to your starter or the connected gears. If the short is to ground (not through the starter motor) you could do VERY unhappy things to your battery (at worst, a fire could result).

I don't want to panic you, but if there was a short once, it will very likely happen again.

Larry
Larry Shoer

Again, thanks to all for the advise and help. Larry, I will replace the switch, and yes you did panic me, so I will order a new one form Moss. By the way the one that is in the car was from Moss and it is not even a year old. Is there someone else that you guys would reommend to by a switch from?
Louis Levin

Abingdon Spares is always another convenient source. Not sure who makes Moss or Abingdon switches. I vaguely recall negative comments about poor quality in new switches within the past couple of years. Perhaps yours is suspect.

You might want to install a separate battery cut-off switch so that there is no possibility of a problem when the car is unattended. (Assuming you operate the manual cut-off switch.) Check the archives for "Battery cut-off switch" for more information. (The switch I used is for sale on eBay for $3.25.)

Larry
Larry Shoer

Louis - complain to Moss; if we don't speak up, quality declines unchecked.

Tom
t lange

This thread was discussed between 19/05/2010 and 22/05/2010

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