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Motorcycle Repair/1979 Yamaha 1100 xs special turn signal and oil light



I have a 1979 yamaha 1100 xs special that I am in the process of getting back on the road.  I am having problems with the turn signals.  when I turn on either turn signal, the front ones come on solid and the back ones do not come on at all.  Also my oil light just started to come on and stay on could this be related to the same electrical issue?  It seems as though the flasher for this bike also runs the indicator lights between the tach and speedometer.  Please help really frustrated.



ANSWER: Hello Tim,

This Bike is before my time (as stated in my profile), so give me some time to find and study
documentation on it. I think that the turn signal circuit is more complicated than usual, due to the presence of a self-cancelling unit.

Till then, try completely disconnect the rear indicators. If turning on the switch light-up the corresponding only front signal, your problem is, rear signals earth connection (black wire).
Connect chocolate and dark-green wires of left and right (respectively) rear signals, their black wires directly to chassis, or better, to battery minus (-) and try the indicators again.

As for the oil light, does it turn on as you turn the main switch on, off when you start the engine and then on again?

Get back to me with results so far and I'll be more precise next time.

Best Regards,

---------- FOLLOW-UP ----------

QUESTION: Hi Lazaros,

My turn signal issue is fixed. It was a bad ground. As far as oil Light it comes on when. You turn key
on and never goes out. I made sure there is the exact amount of oil in bike. I do have another problem,
My headlight and tail light dont work. I dont know if they turn on with just the key or do they come on when
bike is running. Either way they dont come on. Dont know where to start on this issue. Any help will greatly be



Start by checking all fuses and next ALL grounds, because, the oil light could come on, if the ground to the engine is rusted or there are aluminium salts between the terminal and the crankcase.

You should make a ground testing cable, which will help you a great deal.
You'll only need a three-feet-long cable (10AWG / 2.5mm Dia.) and two small crocodile connectors.
Solder or press-fit one connector to each cable end, and you're good to go...

Connect one end to battery minus (-) and the other to the crankcase, and test oil light again.
Bear in mind that, normally, the oil light comes on when you turn the key on, and off when you start the engine.
Do the same with the front and rear lights, one end to battery (-) the other to headlamp/tail-lamp shell.
The lights should turn on regardless of the engine is running or not.

Best of luck,

P.S.: Did you, by any chance, paint the frame? If yes, you should scrub the paint to the metal
everywhere there is a ground attached.

---------- FOLLOW-UP ----------

QUESTION: Hello Again,

SO far all the advice you have given me has been spot on.  I know have turn signals. (Bad Ground)  I now have head light and tail light (Bad fuse connection)  Once all of that was fixed and working properly, the oil light went out.  After running the bike for a few minutes, the oil light is now staying on again.  Is there an oil sensor switch somewhere that might not be working properly.  I am wondering if the switch is malfunctioning?  the Bike sat for 4 years and when I drained the original oil, there was less than a quart in the bike.  My guess is a oil level sensor switch somewhere might be gummed up.  Is there one on this bike and if so where is it located.  If not what else might be causing the issue?


Hello Tim,

Your bike is equipped with an oil pressure switch (not oil level as most Yamaha bikes).
It is located behind the cylinders, on the crankcase, covered with a rubber cap and single-wire
connected. It is of the normally-closed type, meaning that, when no pressure is present, it is "on" and grounds the wire.

To test it, you have to remove it (the light should go off) ground it (light on again) and apply pressure to it's small hole (light off). You can apply pressure, either by compressed air (approximately 1bar) or with a large medical syringe filled with motor oil (no needle inside the hole!!!). You will need various diameter rubber hoses and improvisation to make an air/oil-tight connection.

If the light doesn't go off when you apply pressure, the switch is malfunctioning.
If it goes off, then, there is a problem in your lubrication system, and oil pressure should be checked by means of a pro-grade oil pressure gauge.
Remember to keep the switch grounded while pressure-testing.

Good Luck.
Best Regards,

P.S. The pressure switch has normal thread, so turn counter-clockwise to remove.
    Picture of the switch:  

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Lazaros Ampatzidis


I can help you on EVERY issue involving POST-1980 Japanese Motorcycles plus KTM and Husaberg. My field of expertise includes Engine, Transmission, Fuel system (carburation & EFI),Electrics and Electronics. Maintenance, repair and tuning. Road and off-road suspension tuning. Please don't ask me about non-Japanese Motorcycle, especially American built on which I have low to zero experience.


I'm a rider and hobbyist since childhood. 25 years motorcycle workshop mechanic.15 years motorcycle racing mechanic. In order of experience high to low:Kawasaki,Suzuki,Honda,Yamaha,KTM,Husaberg.

Hellenic (Greek) Technical School.Internal Combustion Engines Engineer. Automotive Electronics.

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