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  1. #1
    Join Date
    Jan 2014
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    Portsmouth NH
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    Starter Solenoid jumper w/diode for trunk mounted Batt?

    Hello Electrical gurus. I am wiring my GM starter in for my trunk mount battery with a Ford style solenoid (LS3 swap into a 69 Camaro). I read that the new GM starters can sometimes run on if you wire them and just jumper from the main starter cable to the solenoid. Therefore it is recommended to separately wire the starter solenoid signal wire both to the S.solenoid and the Ford type in the trunk with the battery, and do not jumper at the starter. This IS how I wired mine.

    However as I was doing it I wondered if you could jumper the main starter cable to the solenoid if it had an appropriate diode in the jumper? What do you electrical knowledgeable folks think? Let me explain, my thoughts are that the starter motor can produce enough current to keep the solenoid engaged when it is jumpered as it feeds back from the starter motor to the solenoid in a jumpered setup. However with a diode it should prevent this. Just my very limited electrical knowledge playing here. Maybe use a diode something like this for the jumper? https://www.amazon.com/MCIGICM-15SQ0...7&sr=8-2-fkmr3

    I was going to research this then figured my project has bigger things to worry about and I have already wired mine.
    1969 Camaro

  2. #2
    Join Date
    Sep 2004
    Location
    Arizona
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    199
    I jumped at the starter, solenoid in the trunk, no problems. No diodes. I don't like to use two solenoids doing the same thing.
    My 2 cents.

  3. #3
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    Jan 2014
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    Quote Originally Posted by oleyeller View Post
    I jumped at the starter, solenoid in the trunk, no problems. No diodes. I don't like to use two solenoids doing the same thing.
    My 2 cents.
    You still have two solenoids doing the same thing when one is jumped. The one jumped on the starter motor has the ability to create a current to keep it energized. It seems sometimes people are experiencing starter run on and like you some people are not. I was just wondering if using a diode in a jumper situation would fix the run on issue.
    1969 Camaro

  4. #4
    Join Date
    Nov 2011
    Location
    Wylie, Texas
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    In order for that diode to be effective it would need to be placed between the starters main terminal and the starters solenoid start input, which means the current rating of the diode would need to be as large as the current required to start the vehicle. This current is upwards of 60A so the diode that you selected would immediately go up in smoke.

    I suppose if you choose a diode with the proper parameters it would work, but there are a few reasons why you wouldn't want to do it one being that you would lose power through the diode that could otherwise be applied directly to the starter. The diode would need to be big enough to connect the trunk wire which is typically about a 1 gauge wire. These types of diodes are pretty expensive. There are also other diode parameters that would need to be considered like reverse breakdown voltage, reverse leakage current, peak forward current ... In short it's not cost effective or a better solution.

  5. #5
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    Jan 2014
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    Thanks for the explanation blitzer. That is why I asked the question. Electrical is not my strong suit. I guess I thought that the diode would only need to meet the current requirements for the solenoid and not the starter. That makes me wonder if it is smart to jumper the solenoid from the starter cable then, wouldn't that potentially fry the solenoid by what you said?
    1969 Camaro

  6. #6
    Join Date
    Nov 2011
    Location
    Wylie, Texas
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    165
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    No it would not, the solenoid only draws the current it needs which is probably less than 1A. The back EMF produced by the starter when the trunk solenoid is turned off is a valid reason not to connect the starter's solenoid to the starter cable. Having said that I'm actually guilty of doing it this way myself, but so far I haven't experienced any run-on but I agree that the potential is there for it to happen.