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Thread: Adventures in Vapor Lock

  1. #11
    Join Date
    Apr 2021
    SF Bay Area


    Makes sense.

    Anyone have part numbers and a wiring diagram for how to wire up a “dead man” switch on the electric fuel pump? You know…the thing that detects a crash or if the car is sideways? I’m guessing it’s more complicated than a mercury switch, right? I wouldn’t want the fuel to cut out if I go 4x4-ing up an embankment or if I slam on the brakes too hard.
    ...d ..__ .........° |°... | ..__....p
    »»└/ | \────┴──┴/ | \─┘≡

    1973 Series 3, 109

  2. #12


    There are safety switches available that will shut off the power to the electric fuel pump on low engine oil pressure, if the engine stops in the accident. The switch is an "ON - ON" switch with a two sets of contacts, one which is closed when oil pressure is 'low' and the other set closed when oil pressure is 'high'. There are three wires on the switch, one out to the fuel pump, one incoming power from the ignition on circuit, and the other incoming power from the start circuit. When oil pressure is low, the out to the fuel pump is connected to the start circuit, so the fuel pump only has power when the engine is cranking. When the engine starts the oil pressure rises swapping the switch contacts and the ignition on power now supplies the fuel pump. If the engine stops the oil pressure drops and the ignition on contact opens stopping the fuel pump. This could be an issue if you have low oil pressure at idle, or if it takes a while for oil pressure to rise such as very cold weather.

    You can find switches with different setpoints. This one is from VDO set at 4 psig:

    I use a relay in the fuel pump power circuit, and use the safety switch wire for relay switching, not the actual power in and out to the fuel pump.


  3. #13
    Join Date
    May 2014
    Marblehead, MA


    I bought a facet electrical pump to solve for vapor lock. I haven’t installed it yet… but my plan is to hook it up to the choke switch/cable. Rationale: I only use the choke to get the vehicle running. Then, I shut it off…

    So if I hooked the electrical pump to the choke switch (pump is only on with choke) - I get to overcome vapor lock but don’t need to worry about crashing and burning (literally).
    1968 Series IIa
    1997 Defender SW (Original Owner - Sold)

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