Cancel That: 1979 Suzuki GS850 Automatic-Canceling Turn Signals Problem

Reader Contribution by Keith Fellenstein
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1979 Suzuki GS850 Automatic-Canceling Turn Signals Problem

Q: I have a 1979 Suzuki GS850 with the infamous automatic-canceling turn signals, and I am having problems with my third control unit. These are either hard to find or expensive, and often both. My first unit came on the bike, which I bought used. It didn’t work. I bought a used replacement unit, which worked until the mounting strap broke, flipping the unit upside down in a rainstorm and ruining it. My third unit (NOS) worked great until this summer when I installed Dyna coils. Now the turn signals will not stay on while the bike is moving unless I hold the button to the left or right — they blink once or twice and shut off. When the bike is stopped, the turn signals work fine. I have two questions. 1) Could the new coils be interfering with the signal controller unit? I double-checked to make sure I didn’t have plug wires touching or crossing the wires from the control unit, but it still seems like too much of a coincidence. Unfortunately, I discarded the old coils so I wouldn’t be tempted to reuse them, since the wires were dangerously cracked. 2) Can I bypass this unit and just cancel the turn signals manually? – David Witt/Hastings, Neb.

A: I didn’t know much about this circuit so I did a little research on the Net to see what I could uncover. I found a great resource at The GSResources and learned a little about the circuit. And what I learned leads me to believe your new coils may be the cause of your problem. There is a small reed switch inside the speedometer that provides pulses to the control unit. These pulses are fed to a timer circuit to control how long the signals stay blinking. What I think is happening is that your new coils are emitting RF interference, which the reed switch circuit is picking up and sending to the control unit. This confuses the timer circuit into thinking enough time has passed to shut off the signals. The trick now is finding a way to stop that RF interference. The first step would be to inspect your spark plug wires. Are they wire core or resistor wire? If they are wire core, I’d replace them with resistor wire and see if that cures it. An alternative would be to use resistor plug caps or plugs. You only need one suppressor in the circuit, so use only one of those — resistor wire, plug caps or plugs. More than one just makes the ignition work harder than it needs to. And yes, you may be able to bypass the module. I’d post a question on The GSResources forum and see what the consensus is. MC

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