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MG TD TF 1500 - 30MPH Warning Light

I know this is not strictly a TD-TF issue, but I know there are knowledgeable people here who will likely have the answer.

How does this light work, and can someone supply a simple schematic to wire one up - I have a chronometric speedo with a terminal on the back for the wire to the light, but I'm sure there is more to this than one wire.

Thanks Octagonally in Anticipation


Tony - The contact in the chronometric speedo is most likely providing a ground for the light. The light would have a second wire to provide 12 volts to it. You might want go to the MG Car Club site and post your question on one of the prewar and/or vintage registers listed there. Cheers - Dave
Daved DuBois

There is a wiring diagram for a TA on the excellent Totally T-Type 2 website at:

The article describes modifications such as electronic ignition and changing to negative earth but the circuit shows the 30 light connection (wire no. 3 from the speedo) which is unchanged.
Dave Williams (TD10254)

Okay, somebody has to ask. What horrible thing happens at 30 mph on a TA?
efh Haskell

Think it had something to do with the speed limit or some such thing.
TOM Maine

When the early T series MG's were in production the national speed limit was 30 MPH in England. Not sure if it applied only within towns and cities, but the light was there to let a driver know if the car was exceeding 30 MPH.

Bobby Galvez

Thanks Folks,
I posted the question here as there is very little traffic on the MGCC forums - this one is one of the most active anywhere.

I am referring to both the disgram at TT2 and the original wiring diagram - our car has a different mix of original and later electrical components, so it's been a case of creating something else.

The problem with both schematics is the lack of an earth connected to the speedo as drawn - it has a bakelite case, and is mounted in a wooden dash, so I really need to know how to secure an earth to the speedo.

Thanks Dave, I had assumed it was providing an earth, but how ?.

Just another puzzle correcting the errors by PO's.


It's grounded by the speedometer cable. See Doug's article.
Mike Hart

Thanks Mike, you're a champion.



PS - Thanks to all on this board - see you in a Pre-War MG one day !.

And thanks once again to Doug Pelton, not only does he provide a great parts service (to Australia too !), but writes such great articles sharing his knowledge.

Thanks Doug.

This thread was discussed between 26/01/2013 and 27/01/2013

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