Suzuki FZ50 - indicator troubles

[bingo.man]

Hi everyone

I have a 1981 Suzuki FZ50 that has some electrical problems. The indicators will only manage one flash before quickly fading out. The head and tail lights are ok, but if I pull the brakes, the indicators don’t work at all.

When it first started happening, I assumed it was the battery (an old 6V unsealed one), so I swapped it for a new AGM one. That did the trick, for a while at least. After about 8 months the same thing started again. I thought maybe the new battery was a dud, so I bought another one, which again sorted the problem, but only for a while. On the advice of a mechanic I swapped back to a new unsealed one, but that one has now gone as well!

In all cases, putting the replacement batteries on to charge, they showed as fully charged after just a minute or two and the voltage read around 6.3V. I’ve never noticed them being particularly hot or anything else wrong with them.

The bike has a separate rectifier and regulator (wiring diagram attached). The rectifier seemed to test ok, but I’m not sure about the regulator.

It only has one wire in and is earthed to the frame, but there’s no continuity through it. When idling, the voltage across the battery reads 8.7V and at full throttle 9.3V, which seems high to me.

I suppose my first question is, do you think it is the regulator? Would that explain the symptoms I’m getting? Does the lack of continuity prove it’s broken?

Is there anything else I can test?

If it is the regulator, I don’t have many options for a direct replacement (without spending £50 on one from the Netherlands), but I don’t know what buy instead. Most of the new ones seem to have a lot more wires going in to them and I don’t know if my setup is positively or negatively earthed. Could anyone recommend one?

Most of them also seem to be regulator/rectifier combos and I don’t whether they would work. I was hoping to keep the bike as original as possible, but working indicators are probably higher on my list of priorities!

Any advice would very gratefully received as I’m getting rather fed up of buying new batteries!

Thanks very much
Jon

[Easy-X]

The circuit diagram looks pretty standard stuff, negative earth BTW.

From what you're saying about the indicators I would go looking for a bad earth, disintegrating wiring insulation and bad contacts: bulb holders and any corroded connectors... depends on how much patience you have. It's possible the flasher unit might be fault but you could test that in isolation off the bike.

The regulator looks to just leak surplus power to earth. What sort of voltage are you getting across it when the engine's running and the lights are on? How much does the headlamp brightness change (if at all) with the revs?

Swapping the rectifier/regulator combo with a combined unit looks like a fair bit of re-wiring.
____________________
Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[bingo.man]

Ok, thanks. I will check the wiring and voltage with the lights on this weekend. I discounted that sort of thing because a fresh battery seemed to sort it.

The headlight brightens quite a lot when you rev it. It's pretty dim at idle though.

If the regulator was working, shouldn't it show some continuity, or am I missing something?

[Easy-X]

What should be happening is if there is low power from the magneto when idling then the battery should be picking up the slack. If there is too much power then the regulator should dump the surplus to earth.

However, examining the circuit diagram again it looks like the magneto has one tap to charge the battery and a separate tap to run the lights. The battery separately powers the brake lights, indicators and parking light - even when the engine is off - but does not power either the headlight/taillight or the CDI.

So in summary the circuit diagram reveals three distinct areas:

Magneto > Rectifier > Battery > brakes, indicators (via flasher)
Magneto > Regulator > Headlamp/Tail lamp
Magneto > CDI > Coil > Spark Plug

It would still be worth seeing if there's a big variation over the rev range across the regulator to see if it is faulty but I'd say the indicator problem is still likely to either be a faulty flasher unit, bad connections or wiring.
____________________
Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[bingo.man]

Thanks for that extra info. My wiring diagram actually makes a lot more sense now.

I’ve managed to get out to the garage and poke around the bike with the multimeter. So I now have a load of readings but not sure what they tell me!

Indicators
Voltage at the battery starts at 6.5V, 5 flashes then dies, as the voltage drops down to 3V. Switch off, voltage slowly returns to around 6V.

Right and left sides behave the same. Bulbs are correct wattage. With one bulb out it does the same thing, it just lasts a bit longer.

Brake light and parking light
Voltage at the battery starts 6.5V, stays on for about 6 seconds then dies, voltage again drops down to 3V. Switch off, voltage returns to around 6V.

I repeated everything again with a battery charger attached (not sure if this proves anything though).

Parking light stays on fine.
Brake light as above but lasts for about 12 seconds rather than 6.
Indicators. Right and left the same. With one bulb out it manages to keep going with the voltage jumping between 6.4V and 5.7V.

Regulator
Regulator with lights off: idle 5.5V AC, rising up to 6.3V AC through the revs, full throttle 0.1V AC

After doing this I noticed that where the regulator is attached to the frame, which I think is the earthing point, it was painted (the whole frame has had bits touched up) and there was no continuity between the regulator and the frame. So I scraped off the paint and cleaned up the regulator to get that working and then got the readings below. After riding it the regulator actually feels warm now, which it never did before.

Regulator with lights off: idle 6V AC, full throttle 6.3V
Regulator with lights on: idle 8V AC, full throttle 5.8V AC

Rectifier measures ok I think.

Voltage at battery: idle 8.2V, full throttle 9V

Do I need a new battery (that has cured the indicator problem before, for a while at least)?

Is the regulator ok?

Is the battery being overcharged?

[Easy-X]

9V is the max charging voltage you'd want for a 6V battery so that should be fine.

If you have a spare bulb kicking about it'd be nice to see if the battery, with nothing else connected, can power the bulb for a while. But it certainly sounds like the battery... again
____________________
Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Robby]

9V does seem high to me, but this is an old 6V system that was cheap 40 years ago, so it may be within tolerance. On a 12V system you expect to see around 14-15V.

By the sound of it, the problem is with the indicators and the other lights are behaving fine. So I would look it two places:

1. Earths. The frame has been touched up, the wiring is old, so earthing is probably poor. Find all of the earth points and clean them up so you have clean metal on both sides, protect with a thin smear of grease.
I would also run an additional earth cable from the frame to the battery.

2. Indicator relay. Cheap modern solid-state relays can fail like you are describing. A few flashes, then nothing. The original relay was probably a bimetallic strip, which can handle a lot more abuse and is a lot less sensitive to voltage.

Clean up the earths first. If it is still misbehaving, try changing the indicator relay. If they are painfully expensive or hard to find, I would go for any original 6v relay from any old bike. Its a simply 2-wire relay normally, nothing special or model specific.

[bingo.man]

Thank you both very much.

I'll get on and replace the battery as it has it's Mot in a month, and anyway, I'm fed up with using arm signals to turn at junctions!!

Then I'll set to work cleaning up the earthing points and the wiring generally and see if that helps.

Do you think the readings for the regulator imply that it's working? Would be useful if I could definitely rule that out.

Thanks again.
Jon

[Easy-X]

Again, from the circuit diagram:

Magneto > Regulator > Head/Tail lamp

If the regulator wasn't working it would either be open circuit in which case your lamps might blow at high revs or closed circuit - lamps not working at all + might stop battery charging.

It's best to get one thing working in isolation:

Magneto > Rectifier > Brake/Flasher/Indicators

...and then move onto the next bit!
____________________
Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[bingo.man]

Ok. One thing at a time. And indicators first!

Cheers for the help!