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MG MGB Technical - Loss of ground

Hi All

Got all set to get my 67 B GT out of the my shop. I have been working on it this winter installing new side windows and having the head redone. Been starting the car on and off throughout.

Got in, turned the key, heard a light "snap" and all went dead. Because I also added a lighter plug, I figured I blew a fuse. All are ok. I checked for electricity at the solenoid and have 12 volts off the positive terminal. But when I push the start button on the solenoid, I get absolutely nothing. There is no power to anything after the connection on the solenoid.

Though I may have had a disconnect at the battery, but all is fine.

If the solenoid failed, would it cause a failure of the entire power system?


Bruce-C

Check the actual posts on the battery for voltage when you try to start. Not the clamps but the posts them selves.. If voltage is good then remove battery cables and clean posts. Corrosion could have set in.
Sandy
Sandy Sanders

"... remove battery cables and clean posts."

And both ends of the cables and check under the insulation at each end of the cables. If you see corrosion or crud built up there, it is time to replace the cables. Cheers - Dave
David DuBois

Bruce. Please allow me to tag onto the others. No, you would not have a zero voltage at the starter solenoid unless your battery was not connected. But, the two sordid individuals who have bothered to answer your questions are, unfortunately, highly qualified to do so.

Bugger.

First step is to organize a good volt meter and a friend. Check the battery voltage on the battery terminals. If fully charged, the battery should read something like 12.5 to 13.0 volts. Then, have the assistant try to start the car (i.e. "turn the key) while you observe the battery voltage. If the battery voltage drops down into the 11.5 volts, or lower, range, you have a bad battery. If not, turn off the ignition switch.

Put the volt meter test probes on the outside of the battery terminal clamps--the ones going to the cables going to the starter solenoid and the chassis ground. Again, request your assistant to turn the ignition switch to the start position and note the voltage readings. They should be between 11.5 volts and 13.0 volts with the higher reading (most similar to the battery terminal reading) being the most desirable. If the voltage on the terminals is more than 0.5 volts less than was obtained on the battery terminals, remove the clamps, clean with baking soda (sodium bicarbonate) and water, wipe dry, and reassemble.

If the readings, at the clamps, is within 0.1 volts, the system is in excellent operating condition and the terminals and clamps do not need to be cleaned. If not, clean the terminals and clamps, then, reassemble.

Hook the volt meter up to the input terminal of the starter solenoid and a ground. Have the assistant turn the ignition switch to the "start position". Voltage should read, as a minimum, 11.5 volts. If not, bad cable or bad cable to terminal clamp connection.

(The terminal clamps which have a groove in the lead, two bolts, and a curved steel portion to attach to the cut off end of a length of copper cable are a problem. Quite often, they will build up sufficient corrosion, or the bolts will loosen sufficiently to prevent a proper connection, that I cannot recommend this form of system. I have had them go bad, far to many times, over the years. A molded on battery terminal clamp and a soldered on end clamp/piece is the only way to go if you want a reliable system.)

A "quick check" of the battery connections is to turn on the head lights and sound the horn. If you do not get a sound from the horn, the problem is the battery or the connections. If the horn, with the head lights turned on, sounds loudly, you have a starter problem.

Les
Les Bengtson

Bruce

Yes if the solenoid goes down itwill have no power at all as this unit supplies all the car.
put a jumper cable on each side of the pos terminal and see if it starts in effect bypassing the solenoid.

Ste
Ste Brown

DAVE..
We have been called SORDID . I have been nominated to another level. Many other adjectives have been laid on me but never SORDID.
Should we be upset or do we demand a DUEL with broken fan belts or wet noodles?
YOUR CHOICE Dave.
Sandy
Sandy Sanders

No factory fuses involved in cranking or running.

Do you have an ignition warning light or headlights? If not you need to check for voltage at the battery posts, connectors, and 12v battery post and a suitable point on the body. That will tell you if the batteries, connectors or battery ground are at fault. If they are all OK then that leaves the connections at the solenoid where the brown wires connect to the battery cable. Be carefull working round here as you will need the batteries connected while you are testing.

If you have a warning light or headlights but they go out when you turn the key to crank then either the/a battery has failed or the above conenctions are failing under cranking load, you will need to do the same tests as above but with the key turned to crank.

If the lights still work when you turn the key to crank then it's either the ignition switch, the white/red wire from there to the solenoid, or the solenoid itself that is at fault.

"if the solenoid goes down itwill have no power at all as this unit supplies all the car" You need to be careful here. The battery cable feeds 12v to the big stud on the solenoid, then either spades connected to that have brown wires on them to feed 12v to the cars electrics and the alternator, or they are on the same stud. If the solenoid winding or contact is faulty it will *not* affect 12v being fed to the cars electrics, only cranking.
Paul Hunt

Sandy - I already have a piece of metal in my leg due to a dual with a splitting wedge on Saturday. I think that I will choose to ignore the complement and hobble on off to the doctor in hopes that he can extract the metal chip by a means other than sticking my leg in a MRI machine and turning it on (I understand that this is a very efficient means of extracting metal from the body but that the exit wound is not very pretty). Cheers - Dave
David DuBois

Ok, Never doubt experience. I visually checked the terminals and all were clean and appeared tight. As in I could not wiggle it side to side. So I am thinking Nah, can't be battery.

But, As soon as I lightly pulled up, the positive terminal moved and power came on.

So, took the terminals off, cleaned them and the ground connection on the body.

All is running perfectly and we will be off for our first jaunt tomorrow.

Back to electronics 101. Just because you have voltage, does not equate to having the amps to run anything.
Bruce-C

Dave, Please stop trying to split wood. First the finger, now the leg. Geez. What's next? What would we all do without your help.

Bruce, Glad you got it figured out, and that it was something simple. We all need lessons on staying away from the dark side when things go wrong.

BTW, the only remaining electrical gremlin on the '63 B, was the horn. It was a simple fix (I'll tell all in a future post), and now it works perfectly!

Cheers,
Greg
Greg Van Hook

"Just because you have voltage, does not equate to having the amps to run anything"

Exactly so, which is why when testing circuits you must test them under normal load conditions.
Paul Hunt

Bruce. Glad you got it sorted.

Dave. I agree with Greg. Self mutilation is not something for us elderly gentlemen to engage in. Let us leave that to the kids.

Sandy. Yes, you bring the wet noodles and I'll bring my daughter's Stroganoff sauce. I have been missing that since she went off to grad school.

Les
Les Bengtson

This thread was discussed between 11/05/2009 and 13/05/2009

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