FYI, the NAPA/Echlin SL144 is the grub screw version. It's strictly an
lbc switch, i.e., 55-63 Austin, 48-64 English Ford, 51-56 MG, 49-64
Morris, 48-64 Rover, 49-64 Singer and 50-64 Triumph. Their SL147 is a
blade terminal switch with a similar lbc list including 57-70 MG.
Bud Krueger
52TD
Dave & Liz DuBois wrote:
> Your problem is burned contacts in the switch. The burned condition
> causes a high resistance and when current is drawn by the light bulbs,
> all of the voltage is dropped across the switch. This is why you see
> a voltage in a no load condition and no voltage when the bulbs are
> hooked up. The contacts are sealed behind a diaphragm, so there is
> nothing you can do to clean them. I am not sure if the Echlin part
> number that Bud quotes is for the T series cars (grub screw
> connections) or for the later MGs with the spade lug connections, just
> ask for a switch for a 54 or 55 TF at NAPA and they will find it
> listed (but not for the Much older TD). I have to disagree with Ted,
> the fitting should be 1/8" British Standard Pipe thread and not
> tapered (all of the pipe threads on the T series cars are straight
> rather than tapered pipe. Some previous owner may have put a switch
> on Ted's car with tapered threads and distorted the fitting. The
> Echlin switches may have an American thread, which is 1 thread per
> inch different from British, and while they will thread together ok,
> there may be enough interference to cause a leak. I always wrap the
> threads with teflon pipe tape to insure a good seal.
>
> I would suggest adding a relay to the brake light circuit to remove
> the heavy current from the brake light switch. The replacement
> switches sold today are extremely light duty and don't hold up to the
> 3 amps drawn by the brake lights for very long before the contacts
> burn again (I have had them burn in just two weeks). This is
> something you can do after your event this weekend and then you will
> not have to worry about the switch in the future. I have a write up
> and drawing for makeing this modification if you are interested.
>
> Good luck,
> Dave
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