Author Topic: Repair self cancelling indicator relay  (Read 140 times)

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Offline sam9

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Repair self cancelling indicator relay
« on: September 12, 2022, 12:55:34 PM »
Hi all, Ive looked everywhere for a repair guide to the dreaded self cancelling indicator relay fitted to many late RD's & XS's of the seventies & eighties. I'm no expert but do have some knowledge of electrics from this era. I've gathered the following info from studying wiring diagrams testing various parts, trail and error & comments from other RD enthusiasts, so for any mistakes or wrong info I give I apologise, so please do not hold me responsible if your bike goes up in a pile of smoke because of this article. If you do notice any mistakes or wrong info please let me know or comment below.

When the indicator switch is operated It connects set of contacts which give a permanent output to the indicator relay,  this output is cancelled or changed when either the indicator switch is pressed in (cancelled) or switched to the other direction, plus after a 100 metres or 10 minutes (which ever comes first) the timer unit sends a negative 12 volt output to the relay which cancels the flashing. The timer output is reset when the indicator switch is operated again. The self cancelling function will not work with after market relays.

This guide is for the Nippon Denso FN257C which is fitted to my RD250D & probably fitted to many other models, this may also be applicable to other relays which have the auto cancel mode controlled by the speedo. This article assumes the speedo still functions by sending a pulse for every revolution the internal drive makes, if not the usual culprit is to replace the reed switch inside the speedo. The reed switch makes a contact every time the magnet passes it, this signal is sent to the timer unit which after a number of pulses or set period of time will send a signal to the indicator unit stopping it from flashing. Should the reed switch need to be replaced new items can be found inside many house alarm door sensors, simply remove the sensor from the housing it comes in & glue or mount in place of the faulty item inside the speedo. This article also assumes the timer box found behind the headstock is functioning.

To open the indicator relay use a pair of pliers peel back the outer edges of the case which covers the circuit board, once done the innards should simply slide out.

Built into the top of the case is a 2000mfd electrolytic capacitor, assuming the battery is fully charged & in good health this capacitor determines the flashing rate of the indicators, the higher the value the slower the flash rate.

The most common fault is the contacts have become dirty or pitted, much like cleaning the ignition points use a small nail file in between the two contacts to clean them.

If the indicators are permanently on usually indicates the armature needs adjusting, see the photo for more info, if the indicators are off when the indicator switch is operated could indicate either dirty contacts or there is a gap between the contacts, the contacts should be making contact with the relay in the off state, again bend the armature to adjust, adjust the armature in tiny increments, the gap between the contacts when the relay is operating is no more than a millimetre.

If the flash rate is so fast that you hear a buzzing noise from the relay or its just too fast to be legal indicates the capacitor has or is failing, it's simple to add another, simply cut the orange wire to the built in capacitor & insert a 2000mfd capacitor across C & B contacts, making sure the polarity for the capacitor is the right way round (positive contact to B & neg(arrow mark on capacitor) to C), if a non polarised capacitor is used the connections can be any way around, capacitors can be purchased from RS components or Ebay etc, you'll need a 2000mfd electrolytic cap rated at 25 volts.

Hope this article is of help.
« Last Edit: September 13, 2022, 08:53:41 AM by sam9 »
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Offline NIRD

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Re: Repair self cancelling indicator relay
« Reply #1 on: September 16, 2022, 06:20:03 PM »
That’s very informative and a great write up.
Well done.
Still haven't got round to my first restoration yet.
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Offline paul n

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Re: Repair self cancelling indicator relay
« Reply #2 on: September 16, 2022, 06:30:46 PM »
Thanks for that write up. Very thorough.
No garage is large enough!