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Electrical mystery after some brake work

Discussion in '308/328' started by flyngti, Oct 14, 2009.

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  1. flyngti

    flyngti Formula 3

    Jul 16, 2009
    1,246
    Snohomish, WA
    Full Name:
    Eric L
    #1 flyngti, Oct 14, 2009
    I just gone done bleeding my brakes. Over the years, brake fluid somehow left the system. Using a handy pressurized brake bleeder, it took about 30 minutes to bleed the system and now the brake pedal is firm as it should be. With the ignition on, the "brake failure" light is no longer on.

    Ok, here's the mysterious part. When I was running the car a few days ago, I noticed that the brake lights were on. I figured that the brake light switch was on the master cylinder and the lack of fluid made the car think the brakes were on so the brake lights were on. Well, after the brakes were bled, I stepped on the pedal and the brake lights did not come on. Hmmm...strange. I then turned the key, expecting the fuel pump to come on, like it aways does. Hmmm...no fuel pump. What the heck? I know some of these cars have electrical gremlins but come one! Maybe it's just coincidence, but why would the fuel pump stop working after I fill the brake system? I took a quick look and the fuel pump fuse is ok. It's getting late so I'll have to look at it more carefully when I get a chance, but I wanted to throw this out there to see if anyone has an idea of what the heck is going on.
     
  2. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
    Along the Verde , AZ
    Full Name:
    Doug
    #2 AZDoug, Oct 14, 2009
    Have you installed Birdmans fuseblocks yet?

    Have you also replaced all the relays?

    You should do both, then come back if it still doesn't work.

    Old oxidized contacts don't conduct electrons well.

    Note that the 113 relay has been superseded by the 151 relay, if I recall correctly.

    Doug
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,876
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #3 Steve Magnusson, Oct 15, 2009
    Last edited: Oct 15, 2009
    1. Measure the voltage at the bottom and top of fuse #1 (brake lights) where the wires attach (relative to ground) with the key "on" and the brake pedal depressed = both should be +12V.

    2. Measure the voltage at the bottom and top of fuse #3 (fuel pump) where the wires attach (relative to ground) with the key "on" and a person sitting in the Driver's seat (if the seat safety switch has not been bypassed) = both should be +12V.

    The results of these 4 tests will indicated whether the trouble lies upstream or downstream from the measurement point for each problem.
     
  4. flyngti

    flyngti Formula 3

    Jul 16, 2009
    1,246
    Snohomish, WA
    Full Name:
    Eric L
    #4 flyngti, Oct 15, 2009
    If I was looking for the next thing to work on, I guess I found it. Sounds like this weekend's project will be to pull my new Birdman fuse blocks out of the box and install them. I'll order up some new relays as well.

    Time to get out the VOM! Steve, I'll do the test as you suggest and go from there.
     
  5. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    2,345
    #5 Paul_308, Oct 16, 2009
    Last edited: Oct 16, 2009
    The singular function of the 'brake failure' relay is to momentarily light and thus test the 'brake failure' light on the dash if you are watching.

    When the key is in Start position the relay is energized and the light is turned on. The relay has no connection to the brake circuit. The reservoir and pressure brake switches can also turn the light on but the relay and switches are otherwise unrelated. The relay could be missing and you wouldn't know it, assuming you are as watchful as the average driver.

    Which is to say, when hard pressed to find a relay, remove the brake relay or seat belt relay, both common 113.

    Not especially superceded...just a marketing jump. The 113 is 30A and 151 is 40A.

    _________________________
    http://www.ferrari308gtbi.com/
     
  6. mike996

    mike996 F1 Veteran

    Jun 14, 2008
    6,876
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    Mike 996
    #6 mike996, Oct 16, 2009
    Last edited: Oct 16, 2009
    Can't imagine it would be safe to replace a 30A relay with a 40A relay unless the wiring was originally sized to handle that load...was it? Seems that if it was, there would have been 40A relays there in the first place
     
  7. rolindsay

    rolindsay Formula 3

    Jul 14, 2006
    1,022
    Houston, TX
    Full Name:
    Rick Lindsay
    #7 rolindsay, Oct 16, 2009
    No problem. The current rating on a relay is not the same as a fuse. On a fuse, it means that exceeding the stated rating will interrupt the circuit. On a relay it is just the maximum safe rating for the contacts. Therefore, just don't go DOWN in relay rating.
     

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