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Thread: LS1 Ignition On & Start Relays

  1. #1
    Super Moderator dave w's Avatar
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    LS1 Ignition On & Start Relays

    I'm trying to remotely help someone with an LS1 engine conversion. The car is a considerable distance from me, but close enough for the internet to reach. The car is a 1968 points ignition system. It appears there IS NOT an Ignition On and Start wire on the steering column ignition switch. It appears the original engine used the starter "R" terminal to supply power to the points ignition coil + when the ignition switch is in "START". The LS1 starter Does Not have a "R" terminal.

    If I remember my "Old Car" wiring correctly, the points system used a ballast resistor to the points coil + terminal when the ignition switch is "ON" and the "R" terminal supplied the points coil + power when cranking or starting the engine. The vehicle owner removed the ballast resistor and used that wire to supply the LS1 injectors and coil packs with power. The vehicle owner has confirmed the engine is not starting because the LS1 injectors and coil packs Do Not have power when the ignition switch is in "Start".

    Back in the "Day" the "R" was called Resistor Terminal. Back in the "Day" the young "know it all" nuts and bolts wrench mechanics that actually read service manuals would say the "R" was for Relay.

    Below is my idea to solve the Ignition On & Start problem using two relays.

    Is this a good plan?

    Is the schematic below correct?

    Thoughts or suggestions are welcomed.

    dave w




    Ign On-Strat Relays.jpg

  2. #2
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    "Back in the day" the ballast resistor was not in circuit during starting, but only was switched into the circuit during running conditions to prevent coil overheating. During starting, the resistor was switched out and the full 12 volts was applied to the coil-not the 8 to 9 volts that the ballast resistor provided.

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    That should work fine.

  4. #4
    Super Moderator dave w's Avatar
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    Quote Originally Posted by Xnke View Post
    "Back in the day" the ballast resistor was not in circuit during starting, but only was switched into the circuit during running conditions to prevent coil overheating. During starting, the resistor was switched out and the full 12 volts was applied to the coil-not the 8 to 9 volts that the ballast resistor provided.
    I'm thinking the starter "R" terminal is the source for the coil when the ballast resistor is bypassed? Usually the voltage available with the starter spinning the engine is less than 12 volts. I'm thinking the available voltage is maybe in the range of 10.5 volts when the starter is spinning the engine, The stater motor is a HUGE draw on the available battery voltage.

    dave w

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    Yes, the R terminal did the bypass.

    Is it a GM? A 68 GM would have an ignition switch that provides ignition power even in the start position.

  6. #6
    Super Moderator dave w's Avatar
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    Quote Originally Posted by lionelhutz View Post
    Yes, the R terminal did the bypass.

    Is it a GM? A 68 GM would have an ignition switch that provides ignition power even in the start position.
    It's a 1968 GM Oldsmobile. I could not find an ignition switch wire that had power in both run and start. I found wires powered with either run or start. Considering the vehicle is half a century old, with multiple owners, it seem likely the wiring is not 100% original.

    dave w

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    Is the key in the column? They sometimes did that when the switch was out of adjustment. It can just be moved up or down the column to adjust.

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    Instead of relays, you could simply use two diodes. Diodes will have to handle whatever the average current is on the device it is feeding but will work fine.

    Brian
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  9. #9
    Super Moderator dave w's Avatar
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    Excellent idea, these should work https://www.mouser.com/datasheet/2/4...ries-63289.pdf

    I'm likely going to use relays, available at Auto Parts Stores. It's an automotive application.

    dave w

  10. #10
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    Use smaller diodes like a 1N4007 to power one relay.

  11. #11
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    I know this is an old thread but I thought I'd add my 2 cents. When I converted my '64 Impala to TBI 10 years ago I only remember having to tap into the purple starter wire (used the "R" terminal on the starter) for a CRANK signal. I recall metering out which IGN wire/circuit stayed hot even while cranking. Pretty sure even TBI requires 12V IGN and CRANK for starting. I would buy a new ignition switch and ring it out, it sounds like the current one has a bad contact. You might even be able to disassemble the old switch and clean it up.

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