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Thread: SMEC brake input question

  1. #1
    boostaholic Turbo Mopar Contributor
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    SMEC brake input question

    OK, quick question for all you SMEC guru's out there. Pin 29 on the 60 way connector is an input from the brake switch. According to minimopar resources, it's just a 12V input to the ECU so the computer knows when the brake is applied. The ECU raises idle speed until the speed sensor tells it the car is about stopped. It's also used to cancel cruise(which I don't have). On the SMEC cars, there is a second set of contacts on the brake switch that this goes to. Is there any reason I can't just tie into the brake signal wire? My 83 doesn't have the second set of contacts on the switch.

    I just don't want to fry anything on this build.

    Thanks in advance for the help.

  2. #2
    turbo addict
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    Re: SMEC brake input question

    I really don't know but if you do go get the 88-9 switch score the little mounting bracket for it too
    I discovered it was different when I put the 88 wireing in my 86 daytona
    the 88 switch would not fit the earlier bracket so I hadda go back and get it

  3. #3
    boostaholic Turbo Mopar Contributor
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    Re: SMEC brake input question

    I have a Daytona brake switch & bracket laying around somewhere from when I converted my Daytona to 5-speed, but it's way different than the L-body version. I looked up an 89 Omni switch, and it way different than the 83(figured that), but not sure it will fit.

    My only real concern is what happens when I press the brake and the truck isn't running? I hope it doesn't hurt the ecu to be fed voltage while it's not "on". I need to look at the wiring diagram and figure out if the 12V feed for the ECU brake circuit is live all the time like the brake light circuit is. That will most likely answer the question...

  4. #4
    Supporting Member Turbo Mopar Contributor zin's Avatar
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    Re: SMEC brake input question

    There is usually a good reason for stuff like this, I'm thinking that there could be a voltage spike due to inductance in the bulbs that wouldn't be there in a "clean" circuit. Not sure if iit's really a likely thing to occur...

    Mike
    "The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry

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  5. #5
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: SMEC brake input question

    Agreed. Plus, if you ever want to add cruise, it'll be there.

  6. #6
    boostaholic Turbo Mopar Contributor
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    Re: SMEC brake input question

    Quote Originally Posted by cordes View Post
    Agreed. Plus, if you ever want to add cruise, it'll be there.
    I see your point, but by the time I get intercooler piping in, I don't know where I would ever put a cruise servo... And the original for the truck was toast. I threw it away.

    Figure if I was able to drive to Memphis last year without cruise, I don't need it...

  7. #7
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: SMEC brake input question

    You can cram the newer style SMEC/SBEC servos anywhere they'll fit. The one in my shadow was basically dangling down on the trans years ago.

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