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Thread: Fried my ignition. Aka electric fuel pump install fail

  1. #1
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    Fried my ignition. Aka electric fuel pump install fail

    I've installed my share of electric fuel pumps using a simple toggle switch to apply power but I'm now in the midst of attempting an install one using a relay and wiring it directly to the ignition switch.

    I originally hooked all the relay pins this way:

    30 = Fuel Pump
    85 = Ignition Switch (to the terminal that has power when the key is turned to ON and ACC)
    86 = Ground
    87 = Fused line to Battery
    87a = Starter Cable side of the starter solenoid (has power when cranking engine)


    My intention is so the fuel pump would receive power from the ignition when the key was turned to ON then when the key is turned to START it will receive power from the starter side of the solenoid during cranking. However when I connected the hot line to 87 I blew the inline 20 amp fuse so I tried it again and again the fuse blew. OK let me rethink this. I decided to change up the wiring configuration on the relay since it was obvious I did it wrong.


    So I decided to reconfigure the wiring this way:


    30 = Fused line to Battery
    85 = Ground
    86 = Ignition Switch (to the terminal that has power when the key is turned to ON and ACC)
    87 = Fuel Pump
    87a = Starter Cable side of the starter solenoid (has power when cranking engine)


    Before I connected 30 to the battery I connected the fuel pump directly to the battery just to see if the pump came on and it did, no leaks too, good. Ok everything else connected, now connect 30 to the battery, fuse did not blow. I turned the key to ON then to START the engine turned over but the cranking sounded weird so I turned the key to OFF. I let it sit for a couple seconds then turned the key back to ON then to START. Dead, nothing. I turned the key to OFF then to ON and went to check on the pump to see if it was on. It was off.


    I used a multi meter to check power to the starter side of the solenoid when the key was turned to START. No volts. Checked the positive side of the coil too. No volts. Checked the ignition switch terminals with the key ON, no volts...yeah, I think I just fried the ignition switch.


    I studied the relay semantic and realized it doesn't have the 87 open, 87a closed like most Bosch relays.
    It has a 87 open, 87a open because 87a is connected to 87. What the heck. Ok I'm going to buy another relay with the standard 87 open, 87a closed and I'm pretty sure I need to buy a new ignition switch too, I just hope I didn't burn up the electronic voltage regulator I just installed.


    I'm considering just hooking up the fuel pump through a toggle switch so I don't burn up another ignition switch but this is my wife's car and would really prefer the pump to turn on when she turns the key on. Aside from not installing the oil pressure safety switch feature what am I doing wrong here.



    Last edited by Joe V; 01-15-2018 at 07:41 PM. Reason: changed font
    Cheers,
    JOE

    --------------------------------------------------

    "After all is said and done, a hell of a lot more is said than done"
    Clark Olmstead

  2. #2
    Silver Hawk Member
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    You might find this useful:

    http://www.rattlebars.com/avalanche/relay_basics.html

    Don't connect 87a to the starter solenoid. Don't connect it at all. 87a is normally-closed to 30 with the relay coil not energized, so in effect you are trying to crank the engine through that 30-amp fuse.

    I put an electric fuel pump into a VW Super Beetle last year, using one of these relays. My connections: 85 to oil pressure switch, 86 to ignition terminal on ignition switch, 30 to fused power via ignition switch, 87 not connected, 87a to fuel pump. In addition, I have a push-button momentary-contact switch in the dash, bridging 30 and 87a. Turn on the key, 86 and 30 both get power. 85 gets ground from oil pressure switch. Relay clicks, breaking the circuit between 30 and 87a. Fuel pump does not run. Crank for 3 or 4 seconds, engine develops oil pressure, fuel pump kicks in, and engine starts, and fuel pump continues to run as long as the engine runs and maintains oil pressure. (If the car is used daily, the engine will readily start on the fuel retained in the carburetor bowl, regardless of whether or not the fuel pump is running.) The push button switch allows me to prime the carb if the car has been sitting for a long time, and the gas in the carb bowl has all avaporated. Turn on the ignition, let the pump run until I hear it slow down, and then crank the engine.

    Note. The oil pressure switch has to be an actual switch, to work an idiot light, and not a sending unit for an electric oil pressure gauge.
    Gord Richmond, within Weasel range of the Alberta Badlands

  3. #3
    Commander Member
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    Joe V;
    I agree with Gordon, for safety you need a oil pressure switch and or a inertia switch.
    I would wire the pump a little different.
    86 to the run position on the ignition switch,
    85 to ground through a 2 wire normally open oil pressure switch and or a normally open inertia switch
    30 to fused power
    Normally open 87
    87a not used
    Once oil pressure is built up the oil pressure switch closes and terminals 30 87 close keeping the pump running
    As Gordon said a 2 wire push button switch across terminals 30 and 87 to prime the pump if needed
    Normally there should be enough fuel in the carburetor to start the engine.

  4. #4
    Silver Hawk Member
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    To be clear, I wired the relay in the Super Beetle the way I did to make use of the existing oil pressure switch. And it does not affect the operation of the oil light, either.
    Gord Richmond, within Weasel range of the Alberta Badlands

  5. #5
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    Here is a circuit that uses an oil pressure operated fuel pump safety switch that allows the fuel pump to run when cranking the engine.


    fuel_pump_wire_copy_1.jpg

  6. #6
    Silver Hawk Member
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    Yes, that Vega switch was engineered to work in that application. Special order part, now, I expect. There are also fuel pump relays that look for a tach signal off the igniton coil to turn on the fuel pump; found on some Euro cars. My setup works with the normally-closed "idiot light" light oil pressure switches found on many, many makes of cars from the '50's through '70's. It would work on '56 through '62 Studebakers, too, (excluding Hawks).
    Gord Richmond, within Weasel range of the Alberta Badlands

  7. #7
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    The three terminal single pole double throw oil pressure operated fuel pump safety switch is readily available from various suppliers, Airtex part # OS75. I ordered one from Advance Auto for about $15.

  8. #8
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    Gord,
    That link has the easiest to understand explanation of a relay I've seen yet. OK so now I have a clearer picture of what I did wrong. I'm going to go ahead and get an oil pressure switch for the ground in addition to a new ignition switch. The priming button is a cool feature but aside from graylarks solution isn't it possible to wire the the relay (87a?) to something so the pump has power only during cranking?
    Cheers,
    JOE

    --------------------------------------------------

    "After all is said and done, a hell of a lot more is said than done"
    Clark Olmstead

  9. #9
    Silver Hawk Member
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    Quote Originally Posted by Joe V View Post
    Gord,
    That link has the easiest to understand explanation of a relay I've seen yet. OK so now I have a clearer picture of what I did wrong. I'm going to go ahead and get an oil pressure switch for the ground in addition to a new ignition switch. The priming button is a cool feature but aside from graylarks solution isn't it possible to wire the the relay (87a?) to something so the pump has power only during cranking?
    Well, you could wire a diode between 87a and the "s" terminal on the starter solenoid (arrow symbol on the diode pointing to the relay). But it isn't really necessary with an oil pressure switch. And engine will normally develop oil pressure within two revolutions if the oiling system is OK. And unless the carb is right dry, it should start on the fuel left in the carb bowl. But of course, moder fuel does evaporate faster, because it is optimized for fuel-injected engines with pressurized fuel systems. But the push button allows you to run the fuel pump with the engine quiet, so you can hear the sound of the pump change once the float needle closes. That way, you can crank with confidence, knowing that there is fuel in the carb. Saves wear and tear on starter and battery.
    Gord Richmond, within Weasel range of the Alberta Badlands

  10. #10
    President Member SScopelli's Avatar
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    Last edited by SScopelli; 01-26-2018 at 09:25 PM.

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