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Thread: Ignition relay.

  1. #1
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    Default Ignition relay.

    After cleaning up the connections in my wiring harness and the glass fuse contacts in my 1980 GS750E it would run much better. But it seems like I have to repeat the process every couple of years.

    So Im entertaining myself with thinking about installing a blade fuse box and a relay for the ignition. I think I want to cut the yellow/white wire returning from the kill-switch to activate the new ignition relay (because I want the kill-switch to still be active).

    But my question is, should the new relay power just the coils (and not the Ignitor)? Or should the new ignition relay power both the coils AND the Ignitor?

    Does the Ignitor draw much current?
    Are both coils drawing current simultaneously?
    Or is one coil off when the other coil is being charged up?

    Thanks in advance for your comments.
    1980 GS750E (bought used June,1983)
    1968 CB350 Super Sport (bought new Oct,1968)
    1962 CA77 305 Dream (bought used Feb,1963)

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    Redman's Avatar
    Redman is offline Forum LongTimer Past Site Supporter
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    Adding such a relay is what has been called the "Coil relay mod". DO a search for that.

    In general: operate the relay with the circuit that presently goes to the ignition coils. (Even if it is a volt or so low, it will still operate the relay). THat circuit is from the ignition fuse and the kill switch that you are concerned about.
    Get the power from the main circuit or right from battery+, thereby avoiding the voltage loss from igntion swtich and a lot of wiring and connectors.

    Had 850G for 14 years. Now have GK since 2005.
    GK at IndyMotoGP Suzuki Display... ... GK on GSResources Page ... ... Euro Trash Ego Machine .. ..3 mo'cykls.



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    Gorminrider is offline Forum Sage Past Site Supporter
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    I wouldn't use an ignition relay. I would however look at the kill switch very closely. Test it for 0 resistance(after zeroing the multimeter) and/or for voltage drop..

    There should be ZERO loss at ANY switch especially a simple toggle like a kill switch...... likewise, all wiring and connectors...(you can test most lengths of wire end to end for VDrop...sometimes you find a crimp/partial breakage in the wire itself...stuff like that)

    The blade fuseboxes are nice but the old glass ones work fine if you buy quality fuses and (again) be sure that all the rivet or whatever connections are ZERO loss.

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    Quote Originally Posted by Redman View Post
    Adding such a relay is what has been called the "Coil relay mod". DO a search for that.
    Thanks Redman. I have done the search. That’s how I got the confidence to try the coil mod. Got it pretty much straight in my mind how to do the mod. But didn’t see exactly what the relay powered. Just the coils, or the coils and the Ignitor. I assume that the Ignitor current draw is minimal, but wasn’t sure.

    One of my versions would be to just unplug the connectors from the coils. That would allow the wire from the kill switch to still power the Ignitor, and plug one of the coil connectors into pin 85 to activate the relay. If I use a five pin relay with two 87 pins ganged, I could make up two short wires that connect each coil to its pin 87 and not cut up the original wiring harness.

    I don’t know if the on time of the coils overlap each other and was wondering if a diode in the two short wires to feed the coils would keep the coil primary from ringing (oscillating) back into the opposite coil ?
    1980 GS750E (bought used June,1983)
    1968 CB350 Super Sport (bought new Oct,1968)
    1962 CA77 305 Dream (bought used Feb,1963)

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    Quote Originally Posted by pdqford View Post
    I dont know if the on time of the coils overlap each other and was wondering if a diode in the two short wires to feed the coils would keep the coil primary from ringing (oscillating) back into the opposite coil ?
    Don't, it's not necessary and adding a diode in the circuit will introduce a 0.7v or higher voltage drop to the coils.

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    Quote Originally Posted by Gorminrider View Post
    I wouldn't use an ignition relay. I would however look at the kill switch very closely. Test it for 0 resistance(after zeroing the multimeter) and/or for voltage drop..

    There should be ZERO loss at ANY switch especially a simple toggle like a kill switch...... likewise, all wiring and connectors...(you can test most lengths of wire end to end for VDrop...sometimes you find a crimp/partial breakage in the wire itself...stuff like that)

    The blade fuseboxes are nice but the old glass ones work fine if you buy quality fuses and (again) be sure that all the rivet or whatever connections are ZERO loss.
    Thank You for the comments Gorminder. Yes, every 3 or 4 years I have to open all the switches and clean and deoxit them, same for the glass fuses and holders, the underside of the fuse block, and various connectors. Even had to unwind the harness cover to find the “hidden T” connector and resolder it. Bike will run like brand new, but eventually it reverts back in 3 or 4 years.

    I found that using the ohm meter gives an idea where the resistance is, but to get the true picture requires testing each circuit under load and measuring the voltage drops when current is going through the circuit. First time I did the test and clean circuits I picked up 2 more volts at the coils. Made a real seat of the pants difference.
    1980 GS750E (bought used June,1983)
    1968 CB350 Super Sport (bought new Oct,1968)
    1962 CA77 305 Dream (bought used Feb,1963)

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    Gorminrider is offline Forum Sage Past Site Supporter
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    Quote Originally Posted by Killer2600 View Post
    Don't, it's not necessary and adding a diode in the circuit will introduce a 0.7v or higher voltage drop to the coils.
    +1. Don't.

    I'm not an expert but I can't see where "oscillation" is a problem greater than the "solution".

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    Just finished doing the coil relay mod on my 1982 GS550L. The results were pretty good but I will hold off saying it was a total success until I've had more time to test.

    I used the $10 relay from amazon and an auto-style micro fuse holder (also from amazon).





    I fastened down the relay using a philip's head screw which holds down the cover to the airbox-filter.



    The yellow "Common" wire from the relay went to the fuse which went directly to the battery + terminal.

    The relay ground went to a chassis ground point.

    I then soldered a female double-bullet connector to the brown wire (the Normally Open wire) and a single-bullet male connector to the red wire (the Activation wire).



    I also cut the orange/white wires on both coils and inserted bullet male/female connectors on the ends (this way the mod is reversible without much trouble - in case the relay fails on me, I just unplug the bullet connectors from the relay and push them back into their original source).

    Once I had all my connectors soldered on, it was just a matter of plugging the red wire from the relay into one of the two orange-white wires coming out of the kill-switch, and plugging the coil's end of the orange-white wires into the double-bullet connector on the brown wire.



    I tested the brown wire for voltage before trying to start the bike and got about 12.3V. I was getting about 10.0V with the original wiring.

    The bike started with half a turn on the crank and ran super-smooth. Much less stumbling on idle and it was able to hold idle at 1100 RPM very well, even when not fully warmed up.

    I also plan on installing a toggle switch for the headlamp. This will allow me to kill the headlamp if I'm starting on a weak battery or to shut it off if I'm having a charging issue or running the grip warmers.

    I'll follow up with some pics if folks are interested.
    Last edited by DimitriT; 04-29-2021 at 05:42 PM.

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    Thank you for your post DimitriT. Just confirms that I’m thinking similar thoughts on how to execute this mod. Difference is I’m still thinking about it while you have actually DONE the mod!

    I, like you, found out that these Suzuki’s run like a totally different machine with near battery voltage available at the coils. ( I tested mine a few years ago with jumper wires to the coils, and WOW.)
    1980 GS750E (bought used June,1983)
    1968 CB350 Super Sport (bought new Oct,1968)
    1962 CA77 305 Dream (bought used Feb,1963)

  10. #10
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    Quote Originally Posted by pdqford View Post
    Thank you for your post DimitriT. Just confirms that I’m thinking similar thoughts on how to execute this mod. Difference is I’m still thinking about it while you have actually DONE the mod!

    I, like you, found out that these Suzuki’s run like a totally different machine with near battery voltage available at the coils. ( I tested mine a few years ago with jumper wires to the coils, and WOW.)
    What's nice is that all this work can be done off the bike.

    The only part of the job which is destructive is the cutting of the orange-white wires on the coils (between the coils and the connectors which attach to the wires).

    Soldering on the bullets to those orange-white wires is a bit tricky since there's not alot of wire to work with and you need the plastic covers to properly shield these connectors which carry voltage.

    Fabrication of the relay and the fuse harness can be done off the bike. The relay comes with plenty of wire attached to it.

    I'll add some pics to my post with more details.
    Last edited by DimitriT; 04-29-2021 at 02:45 PM.

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