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Thread: Head light switch breaker? + master cylinder question

  1. #1


    hey all, the other day while i was driving my 715 the power started clicking on and off about once every minute or so. when it clicks of for a split second i can hear what sounds like a big relay clicking under the dash. it sounds like it is coming from the light switch.

    Is there a breaker or somthing inside the light switch? i was thinking maybe somthing is shorting out in the tail lights and it is causing the breaker to pop every minute or so. it has been converted to 12 volt if that makes a difference.

    is this correct? or is the switch itself faulty?


    Also, i have a master cylider/booster from an 89 wagoneer. the front brakes do not want to work at all. i bled them the other day and they worked for a little, but then stopped again (at the most un-oppertune moment i might add) there are no leaks at all and the wheel cyliders are fine. could this be a condition of a faulty master cylinder? the rears work fine.

    thanks again.

    -Brian M

  2. #2

    Default Lets here what you have other than 715s!

    Brian , The 3 lever light switch has a circuit breraker inside of it. That is the only type of fuse protection that the electrical system has. You must have a short somewhere.
    Need more information about your brake set up. Did it work before or did you just install it ?? Stock 4 wheel drum brakes ??
    If your using a disc / drum master cylinder ( 89 waggy ) , and drum / drum stock brakes, your going to need a 10 psi residual valve in the front line. M1028
    If your not breakin\' something - Your NOT makin\' enough torque !!

  3. #3


    the donor vehicle never really ran and drove, so i dont know if the master cylinder was good to begin with, but the front brakes did work a little. after i bled the brakes (there was a lot of air in the front lines for some reason) i could get all 4 tires to lock up evenly when i hit the brakes, then the fronts gradually stopped working again.

    would a bad seal on the plunger for the front brake circuit allow air into the system?
    where would i get a 10 psi residual valve, and what exactly would it do?



  4. #4


    Ok, First adjust all your brakes. Both front and rear !! Since M715's don't have self adjusters, this must be done on regular basis. Sounds to me like your brakes worked when the system was " pumped up". After sitting awhile , the front brake return springs pushed the fluid back into the master cylinder. This will be multiplied more by how much your brakes are out of adjustment. The 10 psi residual valve will stop the return springs from pushing the extra fluid back. This is why there is a differance between master cylinders for drum and disc brake systems. If you need more info Email me and I'll give you my phone # . M1028
    If your not breakin\' something - Your NOT makin\' enough torque !!

  5. #5


    will do, thanks. if i need any more help i'll send you an e-mail


  6. #6
    Join Date
    Dec 2003
    Lone Pine, CA

    Default Steering joint easy fix...

    Barry's diagnosis sounds good to me. Those valves are available at most big aftermarket places (summit, speedway, jeg's, etc.) as well as the disc brake places like masterpower.


  7. #7

    Default Late model steering shaft install, maybe column too

    under closer inspection earlier today i found the source of the short which was causing the breaker to keep popping. its the brake light switch. both of these problems (the short and the front brakes not working) occured almost at the exact same time. the brake light switch is hydrualic and is located in the front brake line.

    could these 2 problems be related? or is it some strange coincidence?



  8. #8
    Join Date
    Sep 1998
    North Central Wisconsin


    As far as brake operation goes, all the switch does is turn the brake lights on and off...unless it is leaking fluid out or letting air in, then it shouldnt be making an impact to the brake pressure/operation. I would suppose that since brake pressures are pretty high, that it would leak out under pedal application as long as the system can make pressure...if it would leak air in, it seems it would certainlt leak fluid out.
    Might just be a coincidence...though a funky one!!
    Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.

    Pro-choice, that's a LIE, babies don't choose to die!!

  9. #9
    Join Date
    Dec 2003
    Giddings, Texas


    No pedal, would mean no pressure which would mean no brake light switch activation. But, a non working switch or electrical problem would not effect the brakes except for the leaks that have already been discussed.
    Remember if you didn't build it you can't call it yours.

    6.2 powered M715, 5 M1009's, M416, 2 M101's, 2 M105's, 3 M35's, M1007 6.5 turbo Suburban project called Cowdog.

  10. #10


    i found the culprit.

    i took the brake switch off and closer inspection revealed that there was brake fluid inside of the rubber electrical gromet. i replaced the switch, bled the brakes and everythign works good.

    i guess the diaphram innside the switch must have been broken allowing fluid to flow through the diaphram and up through the screw holes that hold the rubber gromet on and into the gromet. thats why i didnt see any leaks, and why the power kept arching out.

    thanks all for the help


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