MG T-ABC

I am in the final stages of restoring my TC

I have a problem in so much that the ignition light will not go out.
I have installed a new wiring loom and have checked it a couple of times to no avail.
I have taken the dynamo to be tested and it came back with an ok
I am not sure how to go about testing the regulator!
Does anyone have any ideas?

George, Make sure all the wires are connected to the regulator. It may look like they're all in and screwed in but one cou;d not be in but being held in place by the others in the "bunch". Don'r ask how I came across this.....

If you take the regulator cover off you'll see two discs. These will move in and out to the magnectic coils below them. On a fast idle gently press each disc to see if it closes and the ampmeter shows a charge. If it does you may be able to use the adjust screws to get the coils to close the circuits but to do the job properly you need an voltmeter to see the voltage as you adjust. If you're not sure and can't get anyone local who can do it it will be a replacement from NTG (or others)

I gather that you do not have a voltmeter. Would make diagnosis a lot easier.

Do you have the correct wattage bulb in the ignition light circuit and is the resistance wire intact around the bulb holder? Wrong resistance in the warning light circuit can lead to misleading behaviour.

Make sure you have the leads connected to the generator correctly. If everything checks out, you may have to repolarize the generator, check the web for instructions.

Most use an analog (old fashioned) voltage meter for testing. DC 0 - 20 volts is good. The regulator and dynamo and ignition issue so much interference that most digital meters fail to give a reliable reading.

An ignition warning light that will not go out can be a serious sign of a short circuit in the charging circuit.

Bulb that works best is about 2.2 volts/0.5 watts.

In answer to your answers

The build holder is new having just been purchased from Moss
I have a volt meter but it is a digital one so I assume I need to go the bulb route?
What do I need to do now?

Not wishing to disagree with Duncan but a digital voltmeter will be OK for the volatge range we need.

To polarize for POSITIVE earth
Your battery's POSITIVE terminal should be connected to the chassis or frame.
Disconnect the D & F wires from the dynamo. Run a wire from the unearthed terminal on the battery (NEGATIVE) and "flash" it onto the F terminal on the dynamo. By flash I mean brush it over the F terminal 2 or 3 times until a small blue spark can be seen.

Your dynamo's field is now polarised for positive earth. Reconnect the D & F wires to the dynamo.

With the engine running at fast idle connect your voltmeter red wire to earth and use a probe on the black wire to test the voltage on A4 terminal of the regulator (3rd from front) to see if it has more volts than the battery. If it has the dynamo is charging. Now test the voltage at terminal D on the regulator. If this isn't the same as the A4 the regulator isn't working. If it is then check the wire from terminal D (yellow) which goes from the regulator to the warning lamp.

Warning lamps work by putting battery voltage to one side and dynamo voltage to the other. When both sides are equal the lamp goes out.

I think the above is correct, i'm sure someone will correct me if I've made a mistake, my memory isn't what it used to be

ed to add that the D wire should be yellow and the F should be yellow with green. However I can't remember which has the larger terminal. One is small and the other is large. Look closely at the terminal screws to ensure they are on the correct way around.

I say most use the analog voltage meter because most cannot find a digital meter with enough shielding against the interference put out by a generator and buzz box (regulator) and ignition etc.

Did you first clean the regulator points and cut out points in the regulator? If you bought a new regulator, the points contacts are meant to be cleaned and then adjusted. If using an old used regulator, same thing. It is helpful to have a battery that is already fully charged and in good condition. Final charge voltages issued by regulator (from dynamo) can be adjusted through road testing. See:
http://mgaguru.com/mgtech/books/pdf/Luc ... _Tests.pdf

Duncan, I used a digital meter on mine and it was fine. Maybe the problem lies with cheap ones. I've got several meters but the one I normaly use has always seemed to give good readings.

I may as well come clean, I cleaned the dynamo and the contacts in the original regulator. All looked well and the dynamo tested OK. I did fit new brushes. However when I started the car I had no charge. I changed the dynamo, still no charge. I then did proper testing as above and eventually found one of the three wires in A4 wasn't actually in the terminal but was being held in by the other two. When I got all three wires in it was charging and has ever since. I did have to adjust the regulator to get in it chraging at the correct revs and not overcharge.

Now you know why I call myself a plonker! In my defence m'lord I was suffering from extreme sleep depravation at the time from yet to be diagnosed sleep apnoea.

TC's Forever says something on the subject, saying if the charge indicator stays on when engine is running to check the cutout, which is on the right side of regulator. It says to check for cutout points action at around 1000 rpm.

Norman- I am using the original dynamo and regulator, also. All Lucas numbers still "match." I did take apart the dynamo and put in new insulating paper and brushes. Fields were fine. Re-cut the space between the copper commutator bars, and found one of the pieces of the armature stack had slipped over and was contacting the row adjacent--so it simply got ground on with a dremel bit. Basically I cleaned important bits up, new bearing/bush and put back together.

Duncan, I suppose dynamos and regulators are a mystery to most folk now.

I think TC's Forever is a bit light on the mechanical side. He responded by telling me about the new book (this was 2 years ago). The new book has more mechanical stuff, even some idiot overhauling shock absorbers.

even some idiot overhauling shock absorbers

Normal, I take exception to that!

Stephen, Can't see why YOU take exception to that, the idiot is me.

My digital meters go crazy if I try to use them on the TC. Analog works great! I suppose some digital meters are shielded better than others.

Norman, makes two of us.............

Could I add some comments from a complete electrical amateur. This is how I proceed, in fact my own TC failed to charge.
1) test battery voltage, (at battery) car not running. Should be almost 12V
2) start car, voltage should increase to well above 12V, if not speed up idle.
3) regulator should close and battery charge, at say 1000rpm if not trace back though the circuit, to find some point that reads over 12V
4) In my case, I quite quickly found 13V at one side of the regulator points, nothing the other side. (from memory the points were closing) simple cleaning with fine emery did not fix this I had to be a bit more brutal to get the points clean.
5) In summary, is the generator producing voltage, is the regulator getting this voltage and is that voltage getting to the battery?

Turn on the headlights and see if the lights get brighter when you rev the engine.