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Technical Oil pressure safety switch wiring help

Discussion in 'The Hokey Ass Message Board' started by hath, Jun 23, 2018.

  1. hath
    Joined: May 23, 2017
    Posts: 25

    hath

    Today I tried my hand at installing a fuel pump relay and oil pressure safety switch, but didn't quite get the result I'm looking for. The fuel pump isn't supposed to run until the oil pressure sensor hits 5 psi, but right now the pump turns the second I hook the ground cable up on the battery, so obviously I've got my constant wrong, but not sure how to make it all work together. This is how I have it right now:

    From the relay:

    30 - to battery +
    85 - to ground
    87 - to fuel pump
    86 - to "C" on oil pressure switch

    From the oil pressure switch:

    NC - to starter solenoid
    NO - to ignition wire

    Any ideas would be great. Thanks.
     
    chryslerfan55 likes this.
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 44,656

    squirrel
    Member

    Disconnect the pump from the relay, while you troubleshoot.

    Connect the battery ground cable. Measure the voltage on each of the three terminals of the oil pressure switch, relative to ground. let us know what you find.
     
  3. Chiss
    Joined: May 12, 2017
    Posts: 222

    Chiss
    Member
    from S.C.

    5 PSI would be pretty Damn Instant on a good Motor, you mite have it rite already.............
     
  4. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    Which terminal on the starter solenoid are you connecting the oil pressure switch to? There shouldn't be any need for a wire to the solenoid if you only want the fuel pump to run when there is oil pressure. If you wire it to the start terminal on the solenoid, the relay will turn the fuel pump on while the starter is engaged which is how many pumps are wired. If you connect it to the battery cable on the starter, the pump will run all of the time.

    Here is the wiring diagram for the relay.
    [​IMG]
    Pressure switch labeling can be vague as to normally open and normally closed by what they consider the normal condition. Some manufacturers consider pressure applied to be the normal condition while others consider no pressure to be the normal condition.
     
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  5. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

    If it were me, I would have 30 to constant 12v, 87 to the fuel pump circuit, 85 to switched 12v, 86 to the OP switch and the other terminal on the OP switch to ground.
     
    Last edited: Jun 24, 2018
  6. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,284

    Kerrynzl
    Member


    swap fuel pump to 87a, When oil pressure light goes out ,it switches off the 85/86 circuit and the relay switches to "normally open" 87a to switch on the pump.
    Use a bypass button to start the car without oil pressure
     
  7. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 883

    sevenhills1952

    I was locked out of posting a private picture, but try this ... I'm combining the two. Top of drawing shows simple oil pressure switch/pump hookup.
    Bottom shows relay circuit. I covered fuel pump in second picture because pump now controlled by relay. Yellow 18 ga. from relay connect to C terminal on pressure switch. 20180624_151120.jpeg 20180624_151201.jpeg

    Sent from my SM-S320VL using Tapatalk
     
  8. hath
    Joined: May 23, 2017
    Posts: 25

    hath

    So that's exactly how I have it wired. I had gotten the schematics online. Even without the key on, when I hook the battery up, the pump is running.
     
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 44,656

    squirrel
    Member

    provide more info about your oil pressure switch. Did you measure the continuity between the terminals? and the housing?
     
  10. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 883

    sevenhills1952

    To troubleshoot unhook the yellow wire that goes to relay. Fuel pump should not run.
    The oil pressure switch the C terminal should get 12v+ when cranking (So fuel pump runs before you have oil pressure) and also power when key is on and oil pressure is over 5 psi. So unhook yellow relay wire...if pump is running and it's wired correctly there's a relay problem. If it doesn't run while it's still unhooked check C on pressure switch. Should be zero, key off, zero key on, +12v while cranking, +12v key on and oil pressure present.
    I assume pressure switch should have a ground, i.e., don't use Teflon tape on threads.

    Sent from my SM-S320VL using Tapatalk
     
  11. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

    Let me add to the rough handwritten schematics. Doersn't get much more simple than this. The round object is your O/P switch. Only has to handle a couple amps for the relay to ground.
    20180625_114907.jpg
     
  12. hath
    Joined: May 23, 2017
    Posts: 25

    hath

    Hey Mr t body, curious why you wouldn't run a wire to the starter solenoid? Also which terminal does 86 go to? "C" "NC" or "NO" on the o/p? Also how would you wire the rest of the o/p being a 3 terminal unit?
     
  13. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

    I guess my issue is I don't WANT the pump to run automatically on cranking. On a carbureted vehicle it's a moot point since the fuel comes from the bowls (assuming this isn't for EFI). That said, you've copied a system you don't understand and can't easily diagnose. I prefer simple and using components for simple functions. By using the O/P switch for a simple "NO" circuit, all you have to do to diagnose it is if there's 12v in key on and if you have a good ground. As far as the relay, use it for what it's intended.... pass the current for the pump and simply ground it to do so.
    I understand the circuit you've used, but there's a lot of complication (both in wiring and diagnosis) that really provides no benefit (to me at least).
     
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 44,656

    squirrel
    Member

    lets see this switch....do you have a part number, or anything? where did it come from?
     
  15. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

    Here's what I believe he's using (switch-wise). safetyswitch_wo_relay.jpg
     
  16. hath
    Joined: May 23, 2017
    Posts: 25

    hath

  17. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 883

    sevenhills1952

    The problem is there are two many people telling him too many things hence the confusion.
    According to Hath he's using a Walbro 255 pump. As per Walbro site that pump draws 15 amps @13.5 volts. Hath wishes to incorporate the relay, probably a good idea since 15 amps exceeds the oil pressure safety switch current ratings.
    When looking at Jegs pdf diagram for both devices you see this is how it works...
    Starting with the oil pressure switch...
    Three terminals, C,N,NO
    C goes to fuel pump
    N goes to starter solenoid
    NO goes to ignition "on" terminal
    So, fuel pump gets power during cranking and also when key is on AND oil pressure is over 5 p.s.i.
    ------------------------------------------------------------------------
    Now the relay diagram...
    Red 10ga. wire to battery +
    Gray wire to ground
    Purple 12ga. wire to fuel pump
    Yellow 18ga. wire to switch (*NOTE!*)
    ------------------------------------------------------------------------
    Now interface them. Extremely easy...the C terminal on pressure switch goes to yellow relay wire (*NOTE!*) above.
    This way the oil pressure switch C instead of going to fuel pump goes to yellow relay lead. Relay is activated when cranking and when key is on IF oil pressure is above 5 p.s.i.
    ------------------------------------------------------------------------
    Troubleshooting... (if there is a problem)...
    Disconnect yellow relay lead
    With voltmeter or test light verify 12v+ power oil pressure switch N only when cranking. 12+ @ NO terminal with key on ONLY (off on accessory & key off)
    12+ @ C when cranking and motor running.

    Fuel pump should be off when yellow wire is disconnected. Pump should be on when yellow connected to 12v+.

    If pump runs, yellow disconnected, be sure relay Gray is grounded. If it still runs...replace relay.

    Sent from my SM-S320VL using Tapatalk
     
  18. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 883

    sevenhills1952

    Please, I mean no disrespect, but there are three problems with this circuit...
    1) it uses a single contact oil pressure switch, this contact is grounded with no oil pressure, therefore the relay only can activate (running fuel pump) when there is no oil pressure.
    2) fuel injection has to have fuel pump running to start...even if carbureted the bowl (s) may not be full after car sits via evaporation
    3) there is no fuse and/of breaker protection
    Sent from my SM-S320VL using Tapatalk
     
  19. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

    I didn't see where he referenced the pump or application, so if that pump is appropriate (EFI), my schematic isn't. I assumed HAMB/carbureted but you know what they say about assuming.....
     
  20. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

    Normally open would not supply a ground to the relay, hence no pump until 5 PSI CLOSING the switch. You're right, I didn't sketch a complete schematic with fuses. I was trying to draw attention to the problem at hand, not an all inclusive graphic. Lastly, if the bowls are empty, it'll only take a few revolutions while cranking to close the switch and start pumping fuel. Even with EFI there are better ways to wire this than was described. I would be more concerned about passing the current for the pump through the O/P switch than anything.
     
  21. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 883

    sevenhills1952

    I standard single terminal oil pressure switch is n/c, so when turning key to on the oil pressure light comes on. The light gets power one side, grounded other side through switch. So key on...light on...start, oil pressure causes switch to open and light goes off. So relay gets it's ground in your circuit only if switch has no pressure.
    With no ground to relay, relay is off...fuel pump is off.

    Sent from my SM-S320VL using Tapatalk
     
  22. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

    I should have included the explanation from post#13
    "By using the O/P switch for a simple "NO" circuit"
     
    Last edited: Jun 25, 2018
  23. farmalldan
    Joined: Sep 4, 2009
    Posts: 139

    farmalldan
    Member
    from Duncan, OK

    I suspect you are connected (or shorted) to the hot, or battery, terminal on the starter solenoid.
     
  24. hath
    Joined: May 23, 2017
    Posts: 25

    hath

    Ok so I did some resistance testing, results were as follows:

    NC to NO = 1
    C to NC = 000
    C to NO = 1
    Switch housing to frame = 001

    I also did some other testing:

    With ignition wire (86)(yellow) disconnected from C on the oil switch, there is no power to the purple (87) or yellow (86) wires at the relay. Not even when cranking. Nor is the fuel pump kicking on.

    When I attach 86 to C the pump turns on, and 87 and 86 get power at the relay.

    When 86 is disconnected from the oil switch NC and C have power when the key is off.

    When the key is on, all three terminals on the switch have power, C, NC, and NO.

    All this said, it didn't lead me to any conclusions, but I'm no electrician either. Does this lead anyone to a conclusions?
     
  25. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

  26. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 883

    sevenhills1952

    Ok so I did some resistance testing, results were as follows:

    NC to NO = 1
    C to NC = 000
    C to NO = 1
    Switch housing to frame = 001
    ------------------------------------------------------------------------
    Is this with oil pressure switch wires disconnected? Huge difference because you're reading resistance through other things. So...
    yellow activates relay when it gets power, you verified all is ok relay forward to pump
    Now pressure switch...
    Reconnect yellow to C (nothing on NC or NO) pump will not run. Now add NC...pump should run only while cranking. Remove NC, add NO...pump should not run with key on (since oil pressure is zero). Be 100% sure C only goes to yellow, be sure NC only gets power when cranking (check this wire before connecting to oil pressure switch).
    Be sure NO gets power only with key on...not while cranking (check this wire not connected to oil pressure switch).
    Note: tape wire ends...be careful nothing shorts while making tests!
    Note: if that pressure switch checks C to NO or NC to NO 1 ohm with nothing connected to it...that switch is defective.

    Sent from my SM-S320VL using Tapatalk
     
  27. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 883

    sevenhills1952

    I'd have to look at it tomorrow. First problem I see through is 7.5amp fuse going to pump will blow since pump draws 15 amps @13.5 volts.

    Sent from my SM-S320VL using Tapatalk
     
  28. sevenhills1952
    Joined: Mar 14, 2018
    Posts: 883

    sevenhills1952

    Hath has half of circuit ok. Yellow disconnected, pump doesn't run...yellow to power and relay clicks, pump runs.
    Problem is with oil pressure switch section.

    Sent from my SM-S320VL using Tapatalk
     
  29. Mr T body
    Joined: Nov 2, 2005
    Posts: 2,103

    Mr T body
    Alliance Vendor
    from SoCal

    Don't bother, it's good. If you have power to the pump key on engine off with it wired this way, only 2 things can cause it...... bad OP switch or bad relay. If you have power to the pump key off, it's a bad relay (make sure you don't accidentally have pump power from 87A as that will cause your condition).
     
    Last edited: Jun 25, 2018

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