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Brake Light Switch

To: "MG T List" <>
Subject: Brake Light Switch
From: "Bill Snyder" <>
Date: Thu, 14 Sep 2006 08:48:56 -0400
Okay, here's the latest update on my TD braking problems.
Last night I decided to test and replace the brake light switch with a
spare that I have. The filler nut was removed from the master cylinder,
covered with cellophane and replaced. Beforehand, I tested the spare.
Using an analog multitester, there was no resistance between the two
terminals. On the car, there was infinite resistance between the two
terminals on the installed switch and the brake lights were on. I
removed the two wires from the terminals and the brake light went off.
When connecting the two wires together, the brake lights illuminated, so
the circuit appears fine. After removed from the car, the switch tested
0 ohms. I installed the spare and connected the wires. The cellophane
was removed from the MC filler nut. The brake lights were off until the
brake pedal was depressed and the brake lights came on. When pressure
was released from the pedal, the brake lights went off. When the pedal
was depressed the second time, the lights went on and stayed on. When
the switch was removed, the lights again went off the the switch tested
zero ohms resistance again. sounds like the system is staying pressurized when the
brake pedal is released. Opening a bleeder on a hind wheel also allows
the lights to go off. With that information, it seems to me that the
problem has to be either in the X fitting where the switch goes, in the
tubing between that fitting and the master cylinder, or in the MC itself
(as in no return of fluid being allowed by the master cylinder).
Can anyone else think of possible scenarios other that the ones
If not, it seems that my next step should be to remove the MC and check
to make sure the the main cup is retracting far enough to allow fluid
return and check for obstructions in the fluid return port. 
Can anyone with more MC experience comment on how to accomplish these
As always, your comments, advice and input are invited, welcomed, and
Bill Snyder
'53 TD

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