3 prong oil pressure switch and electric fuel pump, is a fuel pump relay needed?

Discussion in 'Powerboats' started by sdowney717, Sep 27, 2011.

  1. sdowney717
    Joined: Nov 2010
    Posts: 1,175
    Likes: 84, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    I am converting the boat to a holley red marine electric pump.

    The safety switch I am going to use is a gm 3986857 3 prong oil pressure switch. Has a common, NO, NC prongs.

    Can the electric pump use the switch without a relay OR is the electric load running threw the switch too much for it and it needs a relay?

    The reason I ask is simply I want to replace the current low pressure idiot light switch with this 3 prong switch without a 'T' hookup.
    the 3 prong switch will just be turning grounds on and off. I will put a relay running off the start wire to the starter and that relay will just ground the pump negative wire to make it run. If I do this, then all I need is the one pressure switch to run the idiot light and the pump. The relay will turn on and ground the negative pump wire when the starter is cranked. When the oil pressure builds up, the safety switch will close and ground the negative on the pump and it will run.

    If I dont do this, I will have to put in a T and have 2 pressure switches. I currently have an oil gauge pressure switch, so really then I would have to have 3 oil switches on the block. See what I mean?

    Currently there are 2 oil pressure switches on the block. One for the idiot light-buzzer, the other for the pressure gauge. I dont want to loose the buzzer idiot light.
  2. gonzo
    Joined: Aug 2002
    Posts: 16,654
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    Location: Milwaukee, WI

    gonzo Senior Member

    As long as the switch can take the amperage it should be OK. Make sure that it was not designed to use with a solenoid.
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