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Re: Brake Light Switch

Subject: Re: Brake Light Switch
From: Bob Howard <>
Date: Thu, 14 Sep 2006 09:35:15 -0400
   The switch on the car should have had infinite resistance if it's
working right -- no movement of the needle.  Needle moves when the
circuit is complete.  I'm thinking that you are getting the right
movement on the gauge but interpreting it backwards.  
  Since the lights light when the two wires are connected ( as would be
done with foot on the pedal) that indicates the light circuit itself is
working right. The problem must be, as you suggested,  switch or pressure
retained in the system.  And the switch seems to be OK. 
   It is easier to replace hoses than to R&R the master cylinder.   I
would try that first, in hopes that the hoses are the culprits, though
not ruling out the MC cups. 
   Also, run you fingers over all the metal brake tubing, checking all
the straps and the areas where it enters the clamp screws into wheel
   I don't believe you can see the cup and the return hole inside the MC.
Careful measurement might tell the tale. Comparison with a cup known to
be good, perhaps from another MC or a new kit, might show a difference in
size if the present cup has swollen in the silicone fluid.  
   You have certainly been diligent about this problem; you're about due
for a bit of good luck.

On Thu, 14 Sep 2006 08:48:56 -0400 "Bill Snyder" <>
> 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
> 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
> 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
> 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
> mentioned?
> 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
> tasks?
> As always, your comments, advice and input are invited, welcomed, 
> and
> appreciated.
> Bill Snyder
> '53 TD

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