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MG TD TF 1500 - Amp gauges and dynamos TD

I have a question that begs an answer. When the 30 ampere gaug was introduced was there a dynamo amperage change as well that corresponded to the gauge? If not why, then why the gauge change? If so how does one identify a high output dynamo vs a low output unit? My rebuilt early dynamo doesn't keep up with headlight draw. Since I drive with them on at all times for safety what is the solution?


Bill Chasser
W. A. Chasser

Bill, the 'high output dynamo', the C39PV2, provides all of 19 amps compared to the earlier 17 amps C39PV model. If you insist on driving with lights on you might try a pair of LED driving lights. I'm sure that you'll hear from the alternator folks. Bud
Bud Krueger


A relay would help if you haven't already installed one.

James Neel

I looked up LED sealed beam replacements earlier.
The one I found was over $200 each and they do not look like TD lenses.

If you look in the archives, there were discussions about a "Stealth" alternator.
One that seems to look like a TD generator but is actually an alternator and puts out a lot more current.

They were also expensive but not more than $500.

Jim B.
JA Benjamin

I can find suitable LED headlights over here for about 50. The Stealth alternator disguised as a Dynamo was about 130 last time I checked. Yes you can pay more than double this for an alternator, but the cheaper one seems to be more reliable - its also the one that the MG Octagon Club sells and gives about 45amp.
Dave H
Dave Hill

what's about the c40? Has the TD ever been factory equipped with Lucas c40? I guess the C40 has more than 20 amps.
W. Mueller

Is the C40 the generator the one used on the Frog Eye Sprite which also had a tach drive feature?

I was able to save some amps by converting to LEDs for the front parking lights and the rear tail lights. No turn signals on my car so no issues with the turn signal flasher.
John Quilter

Converting the turn signals to LEDs is almost worthless anyway in terms of battery drain, as they only run for a relatively brief time.
The Stealth alternator also has the tacho drive and is available in Positive or Negative earth. As it looks like a dynamo and has more than double the output it makes complete sense to change.
Dave H
Dave Hill

I thought there have been a lot of reliability issues with the stealth unit. Maybe this is a different set up than what I'm referring to. Is there a website for the stealth unit )

Bill Chasser
W. A. Chasser

Don't know about the gauges, but for driving with your headlights on, it should be able to keep up. You might want to have a look at your voltage regulator adjustment. Could be you just need to up the voltage output a bit, and that will deliver a bit more current. A 1/4 turn?
D mckellar

There were reliability issues with some of the more expensive alternators available but not with the Stealth Dynamator. See the Accuspark website or buy from MG Octagon Club,
Dave H
Dave Hill

D mckllar has a valid point.
I looked up the current draw on a sealed beam headlamp.
The low beam is rated at 35 watts. It has a current draw of 2.7 amps. This calculates out to running at 13 Volts.

Two lamps on low would only draw 5.4 amps leaving a lot of current in your generator.

What does you amp meter say?
If it shows discharging you may have a generator/regulator issue.
If it shows almost neutral you generator is doing its job.

What does you ammeter say with the key on and the lights on low and no motor running.

It should be around 7-8 amps from the calculations and allowing for the ignition and side/stop lamps.

A long as its below about 14 Amps the generator should be able to keep up.

You can measure the generator output with a clip-on amp meter attachment around the generator cable with the lights on and the car running.

That should give you a clue as to its performance.

Jim B.
JA Benjamin

Bill, Jim is right about the TD's ability to power standard sealed beams. The 35W low beams are no sweat whatsoever. Some lamps run the high beams at 65 watts. A pair will still be drawing current that can readily be provided by a decent condition dynamo and regulator. Any engine speed above 2,000 rpm should provide this. Bud
Bud Krueger

Converting turn signals to LEDs is not about the current draw, it's about visibility for both turn signals AND brake lights. So yes, it's well worth doing.

On that basis, yes.
Dave H
Dave Hill

Agree with above. Check regulator per shop manual directions (also on the Moss Motors web site?). Make sure cut-out points are clean and not burned. If that seems OK, make sure brush springs are OK and the brushes are free and making good contact with armature. Of course check for bad grounds, etc. George
George Butz

I did install LEDs for the tail lights for visability/safety. I have not found LEFs for the fronts to act as Marker/turn signals. If anyone knows a specific source I would appreciate it. I am running negative earth. I also put LEDs in the dash. Made a big difference in visibility. I have the reproduction. PL 700 tri bar lights from Moss with what ever build came with them. I had hoped they were halogen but don't think they are. They are certainly not a bright white. I haven't wired my Flamethrowers yet.

I will check the regulator in a few days and report back with my findings once I can get a meter back on it

Bill Chasser
W. A. Chasser


Check my posts you will find a solution for your front indicators.

G Evans

This thread was discussed between 19/11/2016 and 21/11/2016

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