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Thread: Brake light pressure switch

  1. #1
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    Brake light pressure switch

    I put a mechanical brake light switch in my roadster build and now considering a pressure switch for the upcoming coupe build. Was wondering if there are any major downsides regarding a pressure switch? Would it be best to install on the front lines or rear brake lines?

  2. #2
    Senior Member FF33rod's Avatar
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    Pardon my ignorance, what are you hoping to achieve? I've heard them used as part of an ABS or DSC system but not familiar with them used alone. Would have thought that one would know if there's no brake pressure front or back, maybe not so with power brakes?

    Steve
    Gen 1 '33 Hot Rod #1104
    347 with Holley Sniper & Hyperspark, TKO600, IRS, 245/40R18 & 315/30R18, DRL, Digital Guard Dog keyless Ignition

  3. #3
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    Early VW Bug used them and so did some fords. From what I remember in daily use the failure rate was high.

  4. #4
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    I would use the pressure switch to control a relay to the brake lights. Past experience has shown the switch might not handle the current draw.
    Ian G
    5509

  5. #5
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    The way I understand the switch is that it detects the increase in pressure in the brake line as you step on the brake, at which time it closes the circuit and the brake lights light up. The switch is directly wired to the brake lights just as you would wire the switch behind the brake pedal. Eliminates the need for the little switch behind the wilwood pedal. It is not meant to measure or monitor the line pressure per say.

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  7. #6
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    The pressure switches have been used for years in many vehicles and failure rate is low. You can install the switch in either the front or rear brake line as the pressure triggers the switch to close and activate the brake light at very low pressure. You could use the switch to trigger a relay but I can't remember any factory installation that used a relay. I have used pressure switches on dozens of cars, never experiencing failures nor using relays including roadsters and a coupe.

  8. #7
    Member Jim Stabe's Avatar
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    I originally used a GM pickup mechanical pushbutton switch but it failed. I replaced the GM switch and also added a pressure switch - Belt and suspenders.

  9. #8
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    Up to about 1966/67, Volkswagen had a single circuit brake master cylinder that used one 2-prong switch screwed into the master. Around 1968 or so, it's been a long since I worked on and sold parts for them, they came with a dual master cylinder which had two 3-prong switched in the master, one for the front and one for the rear chambers. I don't remember the reasoning for there being a 3-prongs switch though.
    You could install one 2-prong switch for each master that way if one of the masters fails when you apply the brakes the brake lights would still come on. I don't know how the wiring would work in the wiring harness since I haven't built, yet, a Cobra or looked at the wiring.

  10. #9
    Senior Member NiceGuyEddie's Avatar
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    I have one installed in the rear line and I was told by some in the group behind me that the brake lights don't go on unless I am stopping "moderately" fast.

    When I learned to drive, I was told that if the car ahead of you on the freeway has their brake lights on GENTLY put YOUR foot on the brake to illuminate your brake lights. This is not only to be ready for something, but also so hopefully the person behind you will slow down and/or do the same. I do it as automatically as signaling when I change lanes.

    I've confirmed that doing this in the Cobra doesn't illuminate the brake lights - it needs to be at least "somewhat" pressure on the brakes. Manual brake setup, Jeep Master Cylinder, all Wilwoods.

    This probably doesn't help, but I can say it is not failing, it is not leaking. It's been 15 years.

    I don't recall how it hooks to the brake light circuit but it's definitely two wires coming out of the inline sensor.

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