Welcome to our resource for MG Car Information.



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 TD TF 1500 - ammeter rebuild?

Before I installed a new voltage regulator several months ago, my ammeter used to register in the +20-25 amp range when revving the engine or driving under a load. After installing the new regulator, the needle barely moves. When I rev the engine now, the needle goes to about +2 amps with each rev and quickly jumps back to zero. It almost looks like the needle is sticking on the face of the instrument right where it comes through the slot but its hard to tell. Any thoughts on this? Should I have the thing rebuilt and see if that changes anything? If so, any recommendations who best to rebuild? I'm familiar with Nisonger (I used them to rebuild all my instruments 25 years ago).

Thanks much,
52 TD MkII
B Sieling

Bryan - Unless something was done to the ammeter at the same time as replacing the regulator, I would be inclined to suspect the new regulator. Without the engine running, what kind of a reading do you get when you turn the lights on? You should see a good amount of deflection to the minus side of the ammeter when you do that. If you don't then the ammeter would be suspect, if you do, then the ammeter should be good. The other thing to check is the wiring to the regulator, it is real easy to get a wire in the wrong slot or not get a good ground to the regulator. Good luck - Dave
David DuBois

When I turn on the lights, I get approx -5 amps. When I honk the horns I get a tiny tick in the + direction.
B Sieling


It's a very long time (OK OK I've got a few miles on the clock!)since I set up a voltage regulator. My guess is the points are not set to give sufficient potential. ie the voltage output of the regulator is too low to push a current into the battery.
See page N 12 of the workshop manual for voltage set up parameters.

Graham Smith
TD/C 7822
G.D. Smith

So I guess one doesn't just install a new regulator out of the box without some adjustment first? I got my new regulator from Moss and the only instructions that came with it (that I remember) was to clean the points with kraft paper before installing.
B Sieling

Bryan - The negative reading on the ammeter when you turned on the lights would indicate that the ammeter is working (mine showes 15 amps, but calibration is not the best attribute of these ammeters). The horn current comes directly from the battery and doesn't pass through the ammeter at all. I would agree that the regulator is not doing it's job, but I would not go along with the idea that it is the purchaser's responsibility to adjust it properly. It should be returned to the supplier that sold it to you as a defective item (which it is). You should either get a replacement or your money back. If the latter, contact Bob Jeffers at He can build you a solid state regulator in the original housing and it will come to you calibrated properly for your generator. Good luck - Dave
David DuBois

I have rececntly made one good ammeter out of two rough ones. First thing is to be very, very careful when you remove it from the centre panel or you will snap off the fixing tabs. If you do, you will have to refix the meter to the panel with dobs of epoxy putty. You can remove the plated cover from the bakelite back by carefully prising up the pressed down sides - obvious when you examine the thing. Now the bit where I initially messed things up - I attempted to remove the dial by bending the pointer out of the way - it snapped off! If you look at the rear of the bakelite back you will see a very small screw at the fulcrum of the pointer. This is held tight with varnish. Remove this screw and the pointer will be loose and can be lift out safely. You will note the screw has a point and this forms part of the bearing for the pointer. When ou reassemble put a spot of oil on this and adjust so the pointer zeros properly

Jan T
Jan Targosz

Sorry - forgot to mention how to test the meter. Connect the meter to the battery with a headlamp bulb. Amps x Vots = Watts so a 12V battery with a 36W bulb should show 3 Amps on the meter. If you want to see a greater pointer deflection simply use both head lamp bulbs - head and dip. The wattage will be shown on the sides of the bulbs.

Jan T
Jan Targosz

I would think that if the regulator output is too low to push current to the battery I would have low battery problems when I try to start the car, which isn't the case. There has always been enough juice in the battery to start the car. I do keep a trickle charger on it during the winter when I am not driving the car regularly, but not during the driving season.
B Sieling


I'm not sure how much you are running your car right now, or if you have any experience with the new regulator under driving conditions, but keeping your battery on a trickle charger would negate the need to see much of a charge on the ammeter.

Try running your headlamps for an hour with your car motor off, and then starting it up. If you don't see a jump, you might be concerned. Afterall, the regulator is there to provide current to charge the battery when undercharged. The only simple way to know if everything is ok is to discharge the battery a bit. You've already proved that according to your ammeter a full (trickle charged) battery doesn't require much output from your regulator. It is time to test the reverse.

At least by my humble thoughts... but I am not the last word on generator systems. Except for my TD the last one I owned was in a 65 Rambler.

Dave Braun

I've had the new regulator on the car for several months and the ammeter acts the same during the driving season when I am not using the trickle charger.
B Sieling

This thread was discussed between 16/01/2006 and 17/01/2006

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.