MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MG Y Type - A wiring puzzle

I have had continuing problems with charging, two dynamos and two regulators so far since the engine rebuild. The charging stopped again last weekend so back to my friendly mechanics today.

The regulator was significantly melted underneath so had clearly got overheated at some point and the wire to the large resistor had parted company.

The mechanic produced my original regulator which for some unknown reason they had retained (luckily). We replaced the new one with the old one, all correctly wired according to the circuit diagram - and no joy.

However, with a small change in the wiring charging suddenly began, coping with all the lights on full etc. Success.

But, the change in the wiring seems to me (and the mechanics) to be illogical. We have ended up with the thin yellow/green wire going from the field windings of the dynamo to terminal 4 (F) on the regulator (as it should). With the thick yellow wire from the dynamo connected to terminal 5 (D) as it should, nothing works. Remove this wire from 5 and add it to terminal 4 (F) and suddenly charging happens.

Any thoughts on why this works? Is it likely to cause some damage to the regulator (as above) wired in correctly like this? (The previous regulator was also wired incorrectly to make it work.)

Since I have had so much trouble with this sytem I have no idea what "normal" operation is. Prior to the last regulator dying the system seemed to charge full-bore all the time while driving. Is this normal? Should it achieve a full charge and stop charging at some point?

Appreciate any thoughts and assistance,
Puzzled of Wembley
MG

Hello Murry.
Key for cable colours
8 Yellow,From Dynamo to D , 28 Green & Black from Dynamo to F.
10 Yellow & Green cant see where this is used?
Mal.
Malcolm

Murray, there is a full wiring diagram in the Technical Data section of the Technical Centre on the Y Website.

As Malcolm says - the large Yellow wire must go to the D terminal.

Assuming your car has the correctly colored wiring,
White to A3
Black to E
Purple/Black to A4
Yellow to D
Green/Black to F
Purple to A2
White/Purple to A
White/Black to A1
is th correct schema so I am not sure where you are getting an F terminal from. Y 5100 should have the Lucas RF 95/2 control box fitted. Do you have the wrong control box?

What do your Yellow/Green wires go to?

Paul
Paul Barrow

Hi Guys,
The only contention is the large yellow wire which should, as you say and according to the schematics, go from the dynamo to the D terminal on the regulator. However, with it connected that way, no charging happens. Connect it to F and suddenly charging works.

The other thin wire 28 (perhaps mine is a non-standard colour) goes from the field windings of the dynamo to the F terminal on the regulator.

Murray
MG

Murray

Do you have the RF 95/2 regulator? Lets start there. The wiring schema shows how the internals should connect up in the RF 95/2 too.

Once we have established that you are now using an RF 95/2 we can move forward to discuss the wiring. Mis-connecting the voltage regulator can resultin a vehicle fire. With the greatest of respect to your mechanics, I would seek the advice of an experienced Auto-electrician who has a thorugh knowledge of Voltage Regulators.

Paul
Paul Barrow

Murray - Looking through the wiring diagram for the Y Type, there is no yellow/green (10) wire used, so for the moment, that can be stubbed back and ignored. Of far greater importance is your connection of the Yellow wire to the F terminal of the regulator - that needs to be disconnected from the F terminal RIGHT NOW!!!! Driving the car (or even running the engine) with the yellow wire connected to the F terminal connects the output of the dynamo directly to the field and there is no regulation taking place. this means that at high RPM the voltage of the generator will become high enough to burn out the dynamo and probably the wires from it to the regulator. You can test your dynamo following the directions titled, Testing A Dynamo/Generator in the Other Tech Articles on my web site at: http://homepages.donobi.net/sufuelpumps/ You will notice that the two terminals on the dynamo are tied together for this test (which is how you have the wires from the dynamo to the regulator right now. You will also note that the instructions state that the engine revs should be kept low so as not to damage the dynamo. Doing this test will tell you if the dynamo is good (if it puts out at least 20 volts). From there you can troubleshoot the rest of the charging system. My guess is that the second regulator you got was defective. I also agree with Paul - don't take the car back to your friendly mechanic, he may be friendly and great at mechanical stuff, but he is not competent to work on the electrical system. As Paul suggests, find a good auto electric shop, they will be able to diagnose your problem. Cheers - Dave
David DuBois

David,
Thanks for reminding me where I had read a really good article about things electrical - I shall return to it.

I have already changed the wiring back as per the diagram as I had decided that the always-on charging was probably indicating that the regulator was actually being by-passed, so thanks for the confirmation of that.

Paul,
I definitely have the correct RF95 regulator.

If the weather co-operates I will spend another afternoon under the bonnet on Friday.

Thanks
MG

Still on a wireing problem on the dynamo, I am working on the rewiring on my restro project and went in attach the wires to the dynamo. In the rewiring instrucrions it talks about attaching the large leed to the top and small the the bottom. My dynamo has leeds side by side and both small. The engine I have is out of a YT the the number on the dynamo is C45YV GC24 servise #228334 different from The speced dynamo C45YV-3 L1 service #228139.
Where do the two wires go?? ie witch side does the thick yellow and the thin yellow/green left or right.
Frank
Frank Russell

Frank the heavy yellow wire will go to the larger of the two terminals and the yellow green goes to the smaller terminal. Cheers - Dave
David DuBois

The problem is both terminals are the same size.
How doe i know which is which?
Frank
Frank Russell

"The problem is both terminals are the same size"

In that case, you may have to remove the end cover or find some other way to determine which terminal is connected to the field coils (the smaller, yellow green wire goes here). Cheers - Dave
David DuBois

First, I have discovered that I have a very non-standard wiring loom as far as colours go.

So I went through the connections on the RF95/2 and verified that the wires all went to the places they should go and they all do.

So, it being a lovely weekend for a drive, I wired the digital voltmeter into a strip connector which used to power the radio and set off. Pre starting the reading was 12.95V.

When running, the digital meter was flicking wildly all over the place, up to 20v and the rare minus. With the headlights on the fluctuations were much less, steady on around 14 but slowly dropping.

The ammeter showed -18 on idle with the lights on and -10 when driving. With the lights off the ammeter was just under 0 while driving and a little less when stopped with indicators etc going.

At the end of a 112 mile run with lights on full for the last 5 - 6 miles and the engine off, the reading was 12.65V.

My problem is that I have no history of experience with things running correctly to know what is normal.

Reading about the regulators indicates that they don't kick in to charge until the battery voltage is lower than 12 and since my battery is still above this threshold, does the trip suggest that all is working exactly as it should and positive ammeter readings will come if and when the appropriate time comes?

Dave, your words of wisdom will be appreciated.

Thanks
Murray
MG

Make sure that the earth wire from regulator 'E' is making good contact with the chassis and all the other earth contacts are secure. I had this problem and I concluded that electrolysis action had corroded the contact even though the wire was secure. Clean thoroughly and re connect with a little grease
Bryan

This thread was discussed between 29/08/2008 and 25/09/2008

MG MG Y Type index

This thread is from the archives. Join the live MG MG Y Type BBS now