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Thread: '73 R75/5 LWB won't start, battery fine.

  1. #16
    Registered User lmo1131's Avatar
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    If that is an actual picture of what you have in your hand, it is a 5-pin "changeover" relay.

    30 - common (12v power in)
    85 - coil (from the switch)
    86 - coil (from the switch)
    87 - NO (normally open)
    87a NC (normally closed)

    With power to the relay (30), current will pass through and exit terminal 87a

    When the switch is energized power from 30 will pass through the relay and exit terminal 87

    Note: Either 85, or 86 would be grounded (this circuit energizes the magnet that actuates the contacts inside the relay); it doesn't make a difference which one is grounded.

    As an example, this relay can be used to control high/low beam ... 87a energizes the low beam. When the switch is applied the contact changes the relay over to 87

    "It is what you discover, after you know it all, that counts." _ John Wooden
    Lew Morris
    1973 R75/5 - original owner
    1963 Dnepr

  2. #17
    Registered User lmo1131's Avatar
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    DISCLAIMER: Proceed at your own risk. This is provided as reference only.

    The original relay was wired:

    - #15 -- green/black
    - #30 -- red
    - #31b -- brown/black
    - #87 -- black
    - #D -- blue
    On the new relay...

    30 - red (RT), from the main switch (was connected to 30).
    85 - brown/black (BR-SW) from the starter switch (this connects to ground at the main switch (was connected to 31b)).
    86 - green (GR), this comes from the horn and provides power to the coil in the relay (was connected to 15).
    87 - black (SW) to the starter (was connected to 87).
    87a - leave blank.

    "D" is part of the starter protection circuit

    But there's a catch... the blue (BL) wire from the diode board (to terminal "D") must remain connected with the alternator indicator lamp... of the alternator will not function (that's why there is a double terminal on the OEM relay)

    Here's a close up of what's going on inside the OEM relay...



    Slash 5 diagram.jpg

    Ref. > https://www.12voltplanet.co.uk/relay-guide.html
    "It is what you discover, after you know it all, that counts." _ John Wooden
    Lew Morris
    1973 R75/5 - original owner
    1963 Dnepr

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