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  1. #61
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    Misread your first post. For some reason I had 85 to switched 12v and 86 to alt. (thinking ahead of what I was reading probably )
    That's why I thought NC as alt stationary would supply ground path and would prime off key whilst cranking ???

    Would that work ?

    Shane.

  2. #62
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    Quote Originally Posted by Gregaust View Post
    I have already set it all up and is running . One car I have is as I say a points triggered MSD , tach signal is fine . The other with billet dist and mag pickup = no go . It does as I say , switches on, runs/primes and shuts off , then gets obviously a tiny feed and starts up again.
    It is working well using the pulse from the spark plug lead .
    Not too sure yet if the 6AL2 is different , I've not got that one running yet .
    Ahh OK Different vehicles..I was starting to wonder if you like changing distributors (especially where they are positioned) lol.
    I have seen the wire wrapped around a HT lead somewhere but it was years ago & from memory the vehicle had LP gas & it was something to do with that.
    The 6AL2 looks completely different.

  3. #63
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    Quote Originally Posted by HPEngines View Post
    Misread your first post. For some reason I had 85 to switched 12v and 86 to alt. (thinking ahead of what I was reading probably )
    That's why I thought NC as alt stationary would supply ground path and would prime off key whilst cranking ???

    Would that work ?

    Shane.
    Yeah with NO that would prime whist key on/engine off but cut fuel when the alt. engaged. With NC it would run until the key was turned on then cut fuel until the alt engaged then it would run again until the engine stalled with the key on.

    85 goes to D+ on alt. & 86 to earth with a NO relay. When the alternator starts charging it engages the relay & switches the fuel pump on. when the alt. stops charging ( engine stall,belt lost,alt. fail, key turned off) the fuel pump is switched off. If you want to prime whist cranking just forward bias a 3 amp diode from the starter solenoid to 85. The diode prevents the exciters going back through the starter solenoid when the engine is running.

  4. #64
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    Quote Originally Posted by Elric View Post
    Yeah with NO that would prime whist key on/engine off but cut fuel when the alt. engaged. With NC it would run until the key was turned on then cut fuel until the alt engaged then it would run again until the engine stalled with the key on.

    85 goes to D+ on alt. & 86 to earth with a NO relay. When the alternator starts charging it engages the relay & switches the fuel pump on. when the alt. stops charging ( engine stall,belt lost,alt. fail, key turned off) the fuel pump is switched off. If you want to prime whist cranking just forward bias a 3 amp diode from the starter solenoid to 85. The diode prevents the exciters going back through the starter solenoid when the engine is running.
    The way I was thinking about it, pin 30 requires a switched input as well, which is kind of pointless.
    The bit that has me buggered though, isn't D+ active with ignition on? Be it from the ign source or alt? Thats how I thought it worked, and that's why its not working in my head?

    Shane.

  5. #65
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    The D+ reads (effectively) 0v when KOEO. This is because the charge light is the load in the circuit. When the key is on power flows from the ign switch to 1 side of the charge lamp. The other side of the charge lamp is connected through the rotor and regulator then to earth. Because the lamp is the high resistance part of the circuit everything after that in the circuit will be effectively 0v. The easiest way to think of it is voltage = electrical pressure.
    When you turn on the tap on your garden hose water flows from the tap to the end of the hose ( no valve or spray fitting on the end). The pressure along the length of the hose is effectively 0 because there is no restriction after the tap. If you put a kink in the hose so the water flow is restricted then the pressure between the tap and the kink will be quite high but after the kink it will be almost nil. Think of the kink as the globe.
    Now when the engine starts the the voltage applied to the ign side of the globe remains at 12v. the small current that flows from the globe through the field circuit is enough to start the alternator charging. When the aternator starts charging the D+ terminal has a voltage equal to the charge voltage applied. What this does is apply an equal voltage to each side of the charge lamp. As there is no difference in voltage the lamp goes out. Both sides of the globe are at 12v. When a relay coil is hooked across D+ to earth the relay won't engage until the alternator starts charging because the part of the curcuit that its connected to isn't "powered up" until the alternator in online.
    sorry for the wall of text. Hope my explanation helps some

  6. #66
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    Quote Originally Posted by Gregaust View Post
    Thanks Elric .

    I don't know if the 6AL2 is the same as the normal 6AL as yet .
    Testing today revealed . A MSD6AL-2 does trigger and run the Gastec relay using the tach trigger wire .

  7. #67
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    So i need to wire upmy fuel pump using the gas safety switch and via a msd 6al2 ignition. Does anyone have a wiring diagram for this set up at all? thanks ryan

  8. #68
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    Quote Originally Posted by Elric View Post
    The D+ reads (effectively) 0v when KOEO. This is because the charge light is the load in the circuit. When the key is on power flows from the ign switch to 1 side of the charge lamp. The other side of the charge lamp is connected through the rotor and regulator then to earth. Because the lamp is the high resistance part of the circuit everything after that in the circuit will be effectively 0v. The easiest way to think of it is voltage = electrical pressure.
    When you turn on the tap on your garden hose water flows from the tap to the end of the hose ( no valve or spray fitting on the end). The pressure along the length of the hose is effectively 0 because there is no restriction after the tap. If you put a kink in the hose so the water flow is restricted then the pressure between the tap and the kink will be quite high but after the kink it will be almost nil. Think of the kink as the globe.
    Now when the engine starts the the voltage applied to the ign side of the globe remains at 12v. the small current that flows from the globe through the field circuit is enough to start the alternator charging. When the aternator starts charging the D+ terminal has a voltage equal to the charge voltage applied. What this does is apply an equal voltage to each side of the charge lamp. As there is no difference in voltage the lamp goes out. Both sides of the globe are at 12v. When a relay coil is hooked across D+ to earth the relay won't engage until the alternator starts charging because the part of the curcuit that its connected to isn't "powered up" until the alternator in online.
    sorry for the wall of text. Hope my explanation helps some
    Great explanation and good info !!!

  9. #69
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    Quote Originally Posted by ryan350 View Post
    So i need to wire upmy fuel pump using the gas safety switch and via a msd 6al2 ignition. Does anyone have a wiring diagram for this set up at all? thanks ryan
    Yes the safety relay is grounded by the mount, has ignition power in one side , power out to fuel pump the other. Take a signal from the tacho feed , split it for the centre terminal .

  10. #70
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    Ok so I ended Up speaking to a mate who is a auto elect as i suck at wiring unless the diagrams are simple! Anyways this is how i ended up doing it using the gas safety switch( i sketched a diagram while he told me how to over the phone haha) This is a very simple way and works fine . Note i also added the momentary switch which does not have to be used but is good if you want to prime the fuel system for first start up or want to drain your fuel tank ect...


  11. #71
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    ryan the only thing i can add to the drawing is the momentary push button can go to the relay 85 pin so you don't have to pull full current through the switch the relay does the work

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