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MG TD TF 1500 - Generator vs Regulator vs ?

I have another problem with my charging system and I plan to follow the test procedures that you recommend, but before I start I wanted to ask a basic question.

But first some background information. About 18 months ago, I replaced my generator after the original unit disintegrated (Bob Jefers was a big help in walking me through the testing). Soon afterwards I installed a new wiring harness and my electrical system has been working flawlessly since. This past summer I installed a new battery, coil, and petronix electronic ignition. So for the past 6 months the car has been running great.

Recently I have encountered problems with charging. A couple of times, the new battery had drained after the car set for a week. I thought the problem was because the new radio/CD player had been left on and it drained the battery. So I finally disconnected the unit since it was hard to hear the music anyway -- that is another story. To make sure I trickled charged the battery and everything seemed fine. The ammeter would show proper charging when I would rev the engine, and the problem seemed to go away.

Last week I drove the car at night and decided to turn on the lights (including a fog light). Immediately the ammeter pegged very negative. Ever since that event the ammeter never goes above zero when I run the car without lights. The ammeter shows a slight negative discharge when the blinker is on, and more when I turn on the side lights, but it no longer indicates positive charging with the engine revving.

So I have two questions. First is it normal for the lights to drive the current load so strongly (pegging the meter)? Second, what would now create a situation where the ammeter would not show positive charging even with the engine revving? Could a problem in the lights have reverse polarized the generator?


Mike Iandolo

That's three Q's!

First is it normal for the lights to drive the current load so strongly (pegging the meter)?
>>> No, you have a dead short in the lights. At's why some of us believe in fuses.

Second, what would now create a situation where the ammeter would not show positive charging even with the engine revving?
>>> You frizzled something.

Could a problem in the lights have reverse polarized the generator?
>>> No, You frizzled something.

FRM
FR Millmore

Under normal conditions, the car should run at 0 or a little + ... even with the lights on (otherwise you couldn't drive your car for extended periods at night).
The ameter should show a tiny - when the fuel pump pumps, or the turn signals blink...
The voltage regulator should adjust for any major use of accessories?
Check your regulator or your generator again?

I wasn't charging when I first got the car...I took the generator apart and 'cleaned' anything brass or copper...cleaned out the little grooves in the armature and it has been fine ever since (not a mechanic, just a cleaner...seems to work most of the time)
gblawson(gordon)

Thanks for responding so quickly. BTW, I have fuses. If I had a dead short, I would have expected to see something melt somewhere. Also I am still able to start the car (several times today) so there is still enough juice in the battery to drive the starter. What would I have frizzled?
Mike Iandolo

Gordon - I will check the generator and regulator tomorrow. The generator is new. The regulator looks original. You mention that under normal conditions the ammeter should be slightly positive. For my normal conditions the ammeter would go very positive at 3,000 RPM. Does this point to a generator problem?
Mike Iandolo

Mike-
"BTW, I have fuses"
>>> Who put them in and where in the circuit are they? It did not come with them in the light circuit.

Potential frizzlees: Mainly the control box, plus whatever caused the short = headlamp/foglamp wiring.

Sounds like your control box or battery was/is already near death. It should act as Gordon said with a good battery. The ammeter indicates power to or from the battery, nothing else. When the car is running, all power used comes from the generator through the connections at the control box, direct to the load, not through the meter.

FRM
FR Millmore

Mike,

I have had the same problem after a long nightime drive.
I just cleaned the contacts in the regulator and every thing worked again. To do this just run a piece of paper several times through each contact while lightly pressing them closed.( with the battery disconnected)

John
J Scragg

FRM,

I am fortunate to have had very few electrical problems with my TD. As a result I am not as well acqainted with the electrical system as I should be. It has always been my belief that all the electical requirements for the car, come from the battery, with the generator keeping the battery charged up. According to your comment above, this is not the case. Could you clarify the situation for me? I like to understand these things, and appreciate any help you can give me.

George Raham
TD 4224
G. L. Raham

George-
Sure, and it's true for all cars. The battery is there solely to feed the system when the charging device isn't doing its job. If you look at the wiring diagram, you will see that all circuits are connected to the gen through the solenoid/start switch, control box or other secondary connections. Nothing is connected to the battery (or ammeter) in any other way. A car will run perfectly well if you remove the battery cable connections, so long as it is running fast enough for the generator to supply whatever power is needed. The battery only supplies power when the demand exceeds the gen output, i.e., when the engine is stopped or running slowly. It is not generally recommended that the battery be disconnected, since it functions as a big electrical damper on the generator or alternator output. Systems with primitive voltage regulation systems will fry things under some conditions, and solid state electronics don't like the voltage spikes that happen without a battery. In times of old, with even less money than I have now, I frequently started a car with a battery borrowed from another, then put the loaner back before the owner - my mother - found out. As long as you kept the no batt car up at fast idle, you could play with it all day.

I once bought a Chevy truck, with a "reliable" Delco system, in contrast to the "unreliable" Lucas ones I always had. The bloody thing left me stranded in the dark and cold a week after I got it - dead alt, couldn't use the lights. After my wife and I damn near froze to death, we fired it up in the morning and drove almost all the way home, until the brake lights on a forced stop finally ate enough power to kill the ignition, 2 miles from home. In that case, all power 'was' coming from the battery.

FRM
FR Millmore

Mike,
Most likley a short or bad ground somewhere.

FOR SURE & RIGHT AWAY DO THIS:

Either install a battery cut off switch or disconnect the battery untill you find the problem.
Do not leave the car parked with it hooked up till you find the source of the problem.

Umless you have added additional fusing to the lights when you did your re-wire there is no fuse in the light circuit on these cars.

A slow meltdown from a short in your lights could result in a fire....do not take that chance.

Many of us run cut-off switches on these cars ..it is just good insurance.

David
David Sheward

Dave,

I do have a shut off switch and I will disconnect the battery until I can check things out thoroughly, hopefully later this week. I will first look for a possible short in the light system, then I will check the generator and regulator.

I did a quick visual check of the wiring for the lights today and did not see anything that could cause a short. I looked in the lamps for any bare wires. I looked at the wiring harness to see if the insulation could have worn away. They all looked good, although I did not look everywhere. As I said before the wiring harness is new and I installed it very carefully, and everything worked fine for the past year, so I did not miswire anything. If I really have a short, it must be due to something wearing away or failing. I am beginning to suspect the switch itself.

I am guessing that I cant test for a short with the multi-meter.

Mike Iandolo

Mike-
It is possible that the lights are a sort of red herring. If the control box went belly up, in reacting to the increased demand of the lights, then it may be only a control box and/or generator or battery problem. The fact that the battery was dying after short sitting periods means that either it is bad, or there was a drain back through the system. I had a brand new battery incinerate an MGB alternator a year ago; had a dead short internal to the battery, after 50 miles. Finding transient shorts is nerve wracking. If it were me, I'd put an in line fuse in the feed to the light switch to be certain that some bizarro fault in the lighting does not make it happen again.

FRM
FR Millmore

hey fellas, could it just be as simple as a bad battery? what if the new sound system WAS left on..the battery is dead flat and recharged. the deep cycle warps plates, internal short or reduced capacity. charging system has all it can do just to pump juice into bad battery and when lights come on the demand is greater than generator capacity and the ammeter pegs out. any thoughts? regards, tom
tom peterson

FRM - I think you may be correct in your diagnosis. I just did a couple more tests and I am now convinced that I do not have a short in my wiring system. However I probably still have a problem with either the generator and/or regulator.

With the engine off, I turned on the running lights and the ammeter indicated that they are drawing approximately 3 amps. When I turn on the head lights (without the fog light) the ammeter indicates that they are drawing approximately 11 amps. I did not add the fog light, but I suspect that the single fog lamp would add 5 more amps of current being drawn. These values seem right and they match a set of readings documented in the archives.

These readings also are very similar to what I saw when I had the engine running which means that the car is not generating enough to overcome the drain due to the lights.

Later this week I will test the generator and the regulator. With regard to your suggestion on the line fuse, I actually already have two line fuses that I installed with the new the wiring harness. I put one on the horn (I don't know what I was thinking) and I put one on the line between the H terminal and the DIP switch (I was thinking that this would take care of any major lighting problem). Do you recommend putting a line fuse anywhere else?
Mike Iandolo

Thank you FRM. I'm still learning after 58 years of ownership. Your explanation was clear and understood.

George Raham
TD 4224
G. L. Raham

Mike-
Yes, those readings are good, and show that the gen is not doing anything.
" between the H terminal and the DIP switch" H on the light switch? If so good, and it rules out a short in that circuit too.
If you've been reading archives, you probably know that I believe in fusing everything. So, put one in the side/tail circuit off the main switch. The foglight is still problematic, depending on whether it draws through the HL fuse. The horns are already fused in the stock setup, as are the IGN controlled accessories.

Tom: No, because if the system actually was operating at capacity before it blew up, that would have shown as full charge on the meter. Also, the battery was not "dead", since he trickle charged it and started the car. Further, radios use very little power. My shop radio ran continuously for as much as a year without charging on a pair of MGA batteries we took out because they were bad (wouldn't start the car) - they lasted nearly 30 years, 24 hours a day, saved a lot of money in dry cells! Modern things do kill batteries after a while, my Dodge pickup takes about 2-3 months with whatever the computer is doing.

FRM
FR Millmore

Mike -- I have seen more than one regulator with the strap connection underneath burned in two. Memory says it was the strap that went to the second terminal from the right (A or A1).

Fortunately that does not preclude converting to solid-state. But a short will ruin a solid-state regulator just as it will a relay type.
Cheers,
Bob
R. K. Jeffers

Mike ,
What bob said "strap connection underneath burned in two" jogged my memory ...I had one years ago that was "bent" just enough that it would short but only when I hit a bump in the road.

Hope I didn't insult you with my last post...sounds like you know what your doing. Unlike me back in the 70's when my Austin burnned to the ground in a rain storm due to unfused headlamp short!

I was worried about you buddy... that was a painfull lesson. If I can keep one other person from learning about it the way I did it's worth a slight insult.

Have a spare regulator you can try?
Think I have one for the TF if it's the same and you want to give it a shot.

Cheers,
David
David Sheward

Dave - I took your advice completely as you meant it and I appreciate the advice that you and many others are wiling and able to give on this BBS. I subscribe to several other BBS for my other hobbies and this is by far the best. The attitude of the members is fantastic and the knowledge is unbelievable.

Before I purchased my TD three years ago I had never worked on a car so I am coming up a steep learning curve which would not have been possible without this BBS.

I am hopeful that I will get a chance later this week to continue my diagnosis. I will check the regulator as you and Bob suggest.

Mike Iandolo

This thread was discussed between 16/11/2009 and 17/11/2009

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