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MG MGA - LEDs Positive Ground

Hello All,
I am seeking a source of LED "bulbs" for the stop/turn signals on my MGA. I want positive ground since I have the original Radiomobile radio and a positive ground Pertronix unit in the distributor. Any advice appreciated, also what #of lumens would work best?
T Heath

I'm also looking for LED's for the dashboard lights. Originals are very dull and useless in the dark.

Any advice appreciated, also what #of lumens would work best?

Help,thanks, Barry

Barry Gannon have a lot of information on whats available. These guys are in Southampton. Look under LED FAQ's and it talks about polarity issues and ways around it.

AR Terry

Hi Tom and Barry,
I have fitted both stop and tail and dashboard Leds from Classic Car LED,s in Somerset. They offer white and warm white for the dashboard bulbs in both positive and negative earth ,they make a fantastic difference you can actually see the speedo and rev counter in the dark. They are very helpful they also supply electronic flasher units in both positive earth to you enable you to fit LED bulbs in the flasher units
Duncan Richards is the company owner and he can be contacted on


Thank you Alan and David for your advise. I have asked for a price to supply and ship 'down-under'.

Barry Gannon

I will follow up. Much appreciated.
T Heath

Full LED light boards for all models of the MGA and most other MGs to 1962 and classic Minis are available at
USA made.
Lew Palmer

Does anyone know when you fit LEDs for the dashboard gauges whether the panel light rheostat still has the dimming effect? I suspect it won't with LED currents being much lower.................Mike
Mike Moore

Panel light rheostat does not work at all with LEDs. They will remain bright at all times.

But you can replace the old rheostat with one of these

or this

But you do need dimmable LEDs attached, otherwise the LED driver will just either switch off or flicker as the power is reduced

try these

And all this will require a polarity change as the dimmable bulbs don't appear to exist for +ve earth

Incidentally this bulb gets a great review for the direction indicator tell-tale light on the MGA!
Dominic Clancy

same bulb available with free shipping in singles here

Dominic Clancy

Thanks for all the info. Parcel of bulbs arrived from UK today so I will attempt to fit them asap. I will report performance.

Barry Gannon

Why do you have to go to the trouble of having a complicated electronic circuit just to dim an LED in a simple DC circuit?

Why not just replace the panel light rheostat with one similar but having a higher resistance to control the much lower current levels?

I appreciate that the diode characteristic has a 'knee voltage' of a couple of volts or so below which the diode doesn't conduct in the forward biassed direction and the consequence of this is that you won't be able to dim the light intensity to zero at low light levels. But most people don't want to dim the light from low light levels to zero. If the light is too bright at low light levels then the LED is too big to start with.

Has not anyone installed a dashboard LED while replacing the variable resistance control with one of higher resistance, maybe a carbon potentiometer as the currents are low? Perhaps choosing a resistance value of say 50Kohms. This would be in addition to a fixed series resistance of say 6K assuming the diode takes 20mA at full intensity.

I'm just talking here of trying out one LED for starters.

My only worry would be finding a pot. with a shaft suitable for the original panel knob! ..........................Mike

Mike Moore

Replaced the dash bulbs today. Checked each one by attaching a ground lead before fitting it into place under the dash -- all tested OK.

But -- the two main dials, the speedo and the rev counter, do not light up in place. Neither does the high beam. Do I have an earthing problem?

Comments/solutions please. Barry
Barry Gannon

Expect the ignition light to work. It has two wires, not grounded.

The other lights need ground. Each of the four dash instruments should have a black wire from the harness attached to a mounting bracket screw.

Thanks Barney. I gave the black wire a shake and all are now working well. The LED supplied for the high beam indicator came with a blue light - very fancy - but not bright enough to show through the red jewel, so I swapped it for the white bulb in the map light. I very rarely use the map light and now it has an attractive blue beam.

Night time driving is now enhanced and very much safer. I recommend the change to LED's. Barry.
Barry Gannon

I ordered 4 low profile LEDs from ebay and they dim just fine with the stock dimmer. I got 4 of them delivered for $3.99. Had them since May and they are working fine. Extremely bright too. Now I can see the flasher jewel in the sunshine! Find them here: .


P.S. negative ground only.

Jerry, I'm interested in your findings relating to LED dimming because I bought a set of dashboard LEDs from the outfit that David Speake recommended. I haven't fitted them in the car yet but I've been doing some bench tests on them.
Assuming the panel light rheostat is around 20 ohms I didn't find adding this resistance in the circuit was sufficient to really dim the LED light intensity.
There was a noticeable change in intensity but with 20 ohms in circuit the LEDs were still very bright.
The observation is a bit subjective I admit and it would be best to try it out at night in car. However, I came to the conclusion that a 1.5K ohm potentiometer would be the minimum resistance required for reasonable dimming.

Because the large gauges are illuminated internally and the small gauges externally two different types of LED lamp are supplied in the MGA dashboard kit. Unfortunately the two lamps with their differing numbers of LEDs 5 SMD and 8 SMD have different I-V characteristics and the simple resistive dimming circuit dims the two types of lamp differently.
So to achieve good even dimming of all four LED lamps they should be the same type.

A question I'd like to ask is that with your setup, with all four low profile LED lamps, is the dial illumination even and adequate for both small and large gauges?

Thanks ................. Mike
Mike Moore

I am satisfied with these for both applications. They are very bright and work well on the oil/water and fuel gauges. In fact there is quite a bit of light spill from these. One caveat - I may not be as critical as you are.


This thread was discussed between 08/09/2017 and 09/10/2017

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