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MG TD TF 1500 - Alternator from Ford Transit

I am considering fitting an alternator to my TF. I propose to use one from a Ford Transit - the one where the armature shaft sticks out at the rear. This will enable me to make up an adapter for the tacho drive. I've seen these for sale at about 30. I have a few concerns though. I realise the main feed from the unit to the battery will need replacing with a much thicker wire but why do alternators have two feed wires? (plus the one that goes to the warning lamp). Also alternator equipped cars use a volt meter rather than an ammeter. Why is this? and what do I do about the ammeter on the TF. The Transit alternator would probably bend the needle at full charge! Should I simply disconect it and rely on the warning lamp? For the tacho be work properly I will have to use a drive pulley with a diameter as the original dynamo. Will this be OK with an alternator? I know replacement alternators are available that look exactly like a Lucas dynamo but they are very expensive and I don't know if they have a tacho drive. I am now thinking along the same lines as some of the historic building heritage organisations. If they have to replace stonework on say a castle they use new stone, use a master mason to do an expert job but don't attempt to disguise the repair. I will leave my alternator for all to see.

Jan T
J Targosz

Modifying vehicles isnt always simple, this information came from another site I frequent.

"Most alternators will not put out any appreciable amperage until they hit about 1000 RPM. Highest amperage ratings are usually found in the 5-6000 RPM range. ever notice how increadibly small the pully is on your alternator? Like the size of a silver dollar. Alternators are usually made to spin at 3x engine speed. 2.5 would be minimum."

I dont think the generator pulley, to retain tacho calibration will spin the alternator at these revs.

I believe the Ford Transit alternator is rated at 55 Amps and the regulator is fitted internally,the TF Ammeter is not appropriate and you will have to look at increasing the capacity of wiring in the charging circuit. Ammeters are not used where alternators are fitted because of the high currents they deliver.

G Evans


Your question "why do alternators have two feed wires?"
In fact there is only one feed wire, the second is for battery voltage sensing, termed "battery sensing" another method of sensing voltage is "machine sensing" this is done within the alternator.


52 TD
J Scragg

have a look at Totally T Type2 on-line mag issue 2 in October 2010 (see ). There is an article by Malcolm Sayers who has done this conversion to his TD and his TC.
Regards, Brian Rainbow
Brian Rainbow

Hi Brian

It was Malcolm's article that prompted me to consider the Transit alternator. If you Google "MG TD alternator there are photos of a conversion carried out by David Braun which shows a very elegant fabricated pulley and tacho drive. The pulley appears to be similarly sized to the original and Malcolm's conversion uses the TD one. I wonder if the pulley size was reduced it would be possible to recalibrate the tacho by pulling off the finger and reducing/increasing the spring tension. Regarding the ammeter I wonder if it is possible to put a diode in the circuit to block charging and only use the gauge for discharging. It would be great to hear from someone who has carried out this conversion.

Jan T
J Targosz

My TD came with a Bosch alternator fitted by the PO. The rev counter obviously did not work. I did two things, I had the rev counter fitted with an electronic mechanism and now it works and is very accurate. The other thing was to adapt the ammeter to the higher amps. It is the same ammeter but now I have to multiply the reading by 2 to get the real amps. As long as the needle shows positive, I am happy. So, the alternator looks like an alternator, no drive cable to the rev counter but rev counter and ammeter work and look authentic.
Richard TD 0460
R A B Wilson


Unless you just want to do the conversion yourself.

I suggest you contact Jerry Felper at British Auto Electric 2722 E Carnival Ave Anaheim, CA 92806
(714)279-8081 e-mail:

He makes a very nice Negative Ground Alternator conversion kit complete with the tachometer drive and everything you need for the instillation with no alterations to the car. You use the belt thats on the car.

Give him a call or an e-mail.

ECS Stanfield

I isntalled an alternator with tacho drive from Racemettled in UK last winter. Same pulley size as original works like a dream, but probably fried my ammeter / TF type.

I am curious about the diode solution to the ammeter, anybody doing such a conversion on a commercial basis?


Jan Emil Kristoffersen

I've been considering adapting an alternator so that I could have heated seats when I'm done. I probably would just wire the alternator output directly to the battery rather than attempting to run it through the amp meter. I probably will just bypass the amp meter altogether and rely on the idiot light.

I've converted lots of equipment to alternators, some with simple one-wire types although it's pretty easy to wire them as three wire types. On a backhoe I actually added an idiot light and kept the amp meter, which pegs after start but seems to take it OK. The ability to let it idle with all the lights on makes it worth it.

I've finally decided to put an alternator on the last John Deere 2 cylinder I have. I've replaced brushes and bearings and voltage regulators through the years but a $40 dollar alternator will last forever, especially on a reserve machine.

It's too bad that our amp meters aren't external shunt, then we could simply change the shunt to accommodate the extra amps.

It seems that Richard was able to change the internal shunt in his so perhaps he will elaborate.
JE Carroll

>It's too bad that our amp meters aren't external shunt, then we could simply change the shunt to accommodate the extra amps.

While the normal shunt provides only in the range of 100 microamps or a few millivolts to a meter, there is no reason why you could not add an external shunt to your existing set up.

Looking at the TF wiring diagram in the WSM I find that one side of the Ammeter is fed from the battery at the starter switch (This is a brown wire.) However at that point there is another wire that goes to Terminal A1 of the fuse block.
The other side of the ammeter has a brown an white wire that goes to terminal A of the control box (regulator) Both terminals are in close proximity and an appropiate shunt between A1 (fuse block) and A (terminal Box) would reduce the current through the ammeter.
What is an appropriate shunt? I cant measure any resistance with my meter so its less than 0.1 ohm, perhaps less than 0.05 ohms, since I would expect the meter to round up.

Since the distance to the meter and back to the terminals, is in the range of 4 ft., I would start with about 4 ft. of #12 wire.(0.0016 ohms/foot) (#12 is rated to SAFELY carry 20 Amps) Set up a calibrated current drain, something like 10 Amps would be nice. Touch the wire between the two terminals. See haw far the current decreases. Adjust the length of the #12 wire to give you 1/2 or 1/3 the initial reading
Since you are bypassing the additional current, there is no need to worry about overloading the existing wire.

Jim B.
JA Benjamin

Nice Jim, I never thought about simply using a length of wire as a shunt.

On the older airplanes I worked on as a kid, they were old then so now they're truly antique, the meters were were 50 millivolt so one simply chose an appropriately rated 50mv shunt if a larger generator was to be installed. They were generally wired as load meters, 0 to 100% or volt/amp meters that with a push button for the alternate display.

Personally I think a voltmeter gives the best info - if you have the right voltage everything else is fine.
JE Carroll

I didn't have any of the meter pegging or shunting problems some of you mentioned, the alternator came with a built in regulator.

JE by the way the heated seats work great. I installed a set of the carbon fiber type in my TD a couple of years ago for less than $150.00. These are not a high amperage draw. If you want more info contact me


Ed Stanfield
ECS Stanfield

This thread was discussed between 15/02/2014 and 16/02/2014

MG TD TF 1500 index

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