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Thread: brake light

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  1. #1
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    brake light


    Need help. Have a 1958 MGA 1500 and while driving my brake lights remain on. After turning off ignition than turning on again the brake lights remain on without stepping on the brake. However the next day the brake lights work fine until after I drive and use the brakes. They once again remain on.

    Thanks for any help

  2. #2
    RonMacPherson
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    Re: brake light

    Okay, your problem is consistent with a failure in the brake light circuit, i.e. the switch.

    Now I don't know which type your car uses, so I'll offer a generic troubleshooting for both the mechanical(on the pedal stop) and hydraulic.

    First you need to id which type you have. Maybe a parts book or a friend, or just looking under the dash at your brake pedal.

    If it's the mechanical type, they are usually mounted at the brake pedal stop, a bracket that the pedal rests up close to when the pedal is not depressed. You should see a small cylinder with a couple of wires on it. One is battery voltage and the other goes out to the brake lights.

    If so, push in and out on the pedal a few times and see if the switch is being shut off completely, usually a small button inside threaded portion of the switch. A lot of times the switch can be adjusted by loosening the locking nut and turning the switch in(to shut off sooner) or out for desired pedal shut off(make sure you unhook the wires while turning the switch, then reinstall them).

    If not this type, then out in the hydraulic circuits by the master cylinder(follow the piping from the master cylinder) you will find a little stubby switch with two electrical connectors on it. This is the hydraulic brake light switch. No adjustment, just replace.

    Way to determine, is get a voltmeter or test light. Test the wires going to the switch(either type). One wire should have battery voltage to it whenever the fuse is energized(some cars you have to turn the key on, others it's on all the time). Then test the other wire, should be no light, or voltage, UNTIL you press on the brake pedal, then it should light up. Way to temporarily stop battery draw,if the light is staying on, is to unhook the output terminal of the switch. Sometimes easy to get too.

    HTH

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    Jedi Warrior David_DuBois's Avatar
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    Re: brake light

    The MGA uses a hydraulic brake light switch so the first thing I would look for is residual pressure in the brake lines. When you get the constant on brake lights the next time you are out, try cracking the bleader screw just a bit on all four corners and see if this turns the brake light out. If it does, then you need to start looking for the cause of the residual pressure on the brake lines. Start with the brake pedal - check that it is returning all the way up when released (is the pedal return spring still in place and not broken?). I don't know if the MGA has an adjustable actuating rod, but if it does (and even if it doesn't) check that the master cylinder piston is being allowed to return far enough to uncover the relief hole in the master cylinder.

    If residual pressure is not the problem, then a new brake light switch is probably in order. Unless you get the switch from Ron Francis Wiring https://www.ronfrancis.com/showpage.php?page=main.htm the replacement switch (which is available from NAPA, Moss or Victoria British - all equally bad) will not last more than a couple of months unless you install a relay/arc suppression circuit athe same time you install the new switch. For information of making and installing the relay/arc suppression circuit, see my article, Installing a Brake Light Relay at: https://www.mgexperience.net/article...ght-relay.html
    Cheers,
    Dave DuBois
    1953 MGTD
    1966 MGB
    http://homepages.donobi.net/sufuelpumps/

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    Great Pumpkin DrEntropy's Avatar
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    Re: brake light

    and if residual pressure IS there, replace all three flex lines FIRST!

    My money's on the flex lines. [img]/bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif[/img]
    '64 MGB, '67 Lotus Elan S-3 DHC,'69 Lotus Elan +2
    '78 Alfa Romeo Spider-undergoing surgery: O=\*/=O
    '84 300D Turbo-"Diesela"-Now my Daily: Oo|≣|oO
    '02 Toyota Camry- SWMBO's 'new-to-her' Daily. <sigh>
    Chaos & Mayhem PTY, LTD..C.I.O. & Floor Sweepervisor

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    Jedi Knight ronzet's Avatar
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    Re: brake light

    dwnuk,

    Just to offer a suggestion...

    Before you start the messy stuff, remove one of the two wires on the sensor, located on the right side frame adjacent to the starter.

    Use your OHMS meter and check to see if the two posts are electrically shorted without pressure on the brake pedal.

    If open, then ask someone to press on the pedal and see if the circuit changes state, that is goes from open to closed... do this several times to check for consistency. These pressure sensors are pretty bullet-proof but do get flaky once in a while...

    Replacing one of these sensors is a quick and easy repair... [img]/bcforum/images/%%GRAEMLIN_URL%%/smirk.gif[/img]

    Just a less messy test before you start the hydraulic manipulations... [img]/bcforum/images/%%GRAEMLIN_URL%%/cheers.gif[/img]
    Ron,

    The only 'barn finds' I ever have are, well, finding a barn. Here's one I found. Moss probably has parts for it.



    My Cars -- '57 MGA(Gone),'66 B (On The Road!!!)

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    Great Pumpkin DrEntropy's Avatar
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    Re: brake light

    I'll narrow my bet since there wasn't a mention of "pulling" left or right and say: My money's on the ~rear~ flex line. [img]/bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif[/img]


    ...it'll turn out to be th' bloody master cylinder... [img]/bcforum/images/%%GRAEMLIN_URL%%/smirk.gif[/img]
    '64 MGB, '67 Lotus Elan S-3 DHC,'69 Lotus Elan +2
    '78 Alfa Romeo Spider-undergoing surgery: O=\*/=O
    '84 300D Turbo-"Diesela"-Now my Daily: Oo|≣|oO
    '02 Toyota Camry- SWMBO's 'new-to-her' Daily. <sigh>
    Chaos & Mayhem PTY, LTD..C.I.O. & Floor Sweepervisor

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    Jedi Warrior David_DuBois's Avatar
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    Re: brake light

    "These pressure sensors are pretty bullet-proof but do get flaky once in a while... " I would ammend that to say the original pessure sensor is pretty bullet proof, but they do eventually wear out and the replacement sensors aren't even able to withstand a shot from a rubber band gun ( I had one fail in only two weeks).
    Cheers,
    Dave DuBois
    1953 MGTD
    1966 MGB
    http://homepages.donobi.net/sufuelpumps/

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    Jedi Knight ronzet's Avatar
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    Re: brake light

    David,

    My pressure sensor is, from what I can tell, the original 50+ year old one and it works fine...

    Based on your, and others, experience with the replacements.. I just hope I don't need to replace it.. [img]/bcforum/images/%%GRAEMLIN_URL%%/rolleyes.gif[/img]
    Ron,

    The only 'barn finds' I ever have are, well, finding a barn. Here's one I found. Moss probably has parts for it.



    My Cars -- '57 MGA(Gone),'66 B (On The Road!!!)

  9. #9
    Great Pumpkin DrEntropy's Avatar
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    Re: brake light

    Dave has me scared, too. Time was I could count on NAPA for a Q&D switch source. Now it appears that's off th' list. RATS!
    '64 MGB, '67 Lotus Elan S-3 DHC,'69 Lotus Elan +2
    '78 Alfa Romeo Spider-undergoing surgery: O=\*/=O
    '84 300D Turbo-"Diesela"-Now my Daily: Oo|≣|oO
    '02 Toyota Camry- SWMBO's 'new-to-her' Daily. <sigh>
    Chaos & Mayhem PTY, LTD..C.I.O. & Floor Sweepervisor

  10. #10
    Jedi Warrior David_DuBois's Avatar
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    Re: brake light

    It's not NAPAs fault, just lowest bidder. The switch that Ron Francis Wiring sells is rediculously expensive, but apparently it holds up well. On the other hand, for less than $10 worth of parst and about 15 minutes of time, one can make and install the relay/arc suppression circuit, which I'v had on our cars for close to 10 years and have not had a single switch failure, where prior to that I was going through switches in anywhere from two weeks to about three months.
    Cheers,
    Dave DuBois
    1953 MGTD
    1966 MGB
    http://homepages.donobi.net/sufuelpumps/

  11. #11
    Great Pumpkin DrEntropy's Avatar
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    Re: brake light

    Yeah, "way of th' world" now. Who cares if an LBC shunts over brake failure or gets punted from behind by a Hummer.... "Durn'd things are too small anyhoo. Should be off th' road!"

    The relay is a good answer. I thought at first you meant they came apart physically and got a sudden case of th' creeps over that idea.
    '64 MGB, '67 Lotus Elan S-3 DHC,'69 Lotus Elan +2
    '78 Alfa Romeo Spider-undergoing surgery: O=\*/=O
    '84 300D Turbo-"Diesela"-Now my Daily: Oo|≣|oO
    '02 Toyota Camry- SWMBO's 'new-to-her' Daily. <sigh>
    Chaos & Mayhem PTY, LTD..C.I.O. & Floor Sweepervisor

  12. #12
    Jedi Warrior David_DuBois's Avatar
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    Re: brake light

    "I thought at first you meant they came apart physically and got a sudden case of th' creeps over that idea."

    I just went back to see what I wrote and when sitting back in the chair, the i in fail looks like a l. No wonder it gave you a bad moment.
    Cheers,
    Dave DuBois
    1953 MGTD
    1966 MGB
    http://homepages.donobi.net/sufuelpumps/

  13. #13
    Great Pumpkin DrEntropy's Avatar
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    Re: brake light

    We all have our "moments" apparently. [img]/bcforum/images/%%GRAEMLIN_URL%%/smirk.gif[/img]


    Still... gonna plan for a relay'd switch for when the -inevitable- occurs.
    '64 MGB, '67 Lotus Elan S-3 DHC,'69 Lotus Elan +2
    '78 Alfa Romeo Spider-undergoing surgery: O=\*/=O
    '84 300D Turbo-"Diesela"-Now my Daily: Oo|≣|oO
    '02 Toyota Camry- SWMBO's 'new-to-her' Daily. <sigh>
    Chaos & Mayhem PTY, LTD..C.I.O. & Floor Sweepervisor

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