turn signal switch
In the MG T series and the MGA so called electropneumatic trafficator timers are used. Normally, the signal will come for around 20 seconds after you moved the turn signal knob in the wanted direction. The system works quite simple: If the knob is moved, an electrical contact will be closed and air is forced out of a small chamber with a spring loaded piston sealed with a leather cup.
During the signal period, the spring loaded piston draws air slowly back into the chamber through a small hole. The piston is turning a small cam, so that the electrical contact will be reopened.
But this fine piece of technology and craftmanship can (and will!) fail:
In the most cases, the switch will come back immediately without any delay. Reason: the air comes too quickly through the little hole in the back. First aid: In the back of the switch, there is a little hole with a screw in it. If this screw is slightly screwed in, the delay may get the right amount.
Whats to do if this method failed? Then the switch is to disassemble. Take time to note the color of the wires to the ports Battery, Right and Left.
If the switch is removed from the dash, the three srews in front of the switch have to be unsrewed. Then the black plastic cover can be removed from the switch. After removing the three long screws which are holding the switch together (take care because of the spring loaded piston - don't loose the spring). If the srew in the back will be unsrewed, too, take care of the little piece of cotton behind the screw which acts as a seal.
If everything is apart, the piston has to be cleaned with some alcohol. Afterwards, the leather seal around the piston must be treated with vaseline - normally, the leather is very dry, so a pretty rich treatment is welcome.
After reassembling the switch, it should be possible to adjust the correct delay time of 20 seconds with the screw in the back of the switch (dont forget the cotton behind the srew!). If this is not possible, the switch should be disassembled again - some tape under the leather seal will help to press the seal tightly against the walls of the switch.
All pictures courtesy of Andreas Pichler.
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