Non-existent diode

Does anyone know the purpose of the diode on the oil level circuit? I'm putting the electrics together (1980 650 Seca), the plug for the diode has been short-circuited with a bit of wire.
It's a fairly basic circuit, goes from the oil level switch to the plug with missing diode then to the oil level warning light.

 

A diode is like a check valve and only allows current to flow in one direction. I assume it’s on your bike due to the possibility of back current. These are used with low voltage LED lights as well as other electrics.

 

Not sure for that model, but if it is like the USA versions the diode for the oil circuit is there for a good reason; the diode prevents engagement of the starter circuit if the oil level switch is closed because of a low oil condition.

Are you missing the entire diode block? There is likely another diode that is part of that block and it is used for engagement of the headlight relay when the AC generator produces enough voltage to energize the relay.

 

Diode goes between the starter button and oil light. Allows the starter button to ground out the light to test it when pressing the starter button but prevents the oil level switch from acting like the starter button and engaging the starter solenoid. One way gate as previously mentioned.

 

Thanks to everyone who replied, that's all good information. Your explanations make sense, I highlighted the circuit on the attached drawing & it does engage with the starter circuit. I can't see any other diodes so will get hold of Len for a replacement.

 

That jumper will allow the oil light to work when the level is low but the bulb will not light when you press start. The risk is the bulb could be burnt out and you would never know, hence the reason Yamaha designed it with a diode so you can check the bulb when starting the bike.

 

^^^This one^^^

 

you could make one with a diode and resistor

your bike has a very diferent setup for the diode block than US versions. ours operate more items.

you could also encapuslate what you make to help dissapate any heat. there should not be much as both components are a passive circuit.
resistor and diode used for oil light/test unless you are out of oil.

when you drain the oil you can also test the oil level switch by turning on the key to see if bulb lights up

 

It sounds like the diode isn't a critical part so there's no rush to replace, if I can't get hold of a replacement I might have a go at making one. We have a few electricians at my work who are good with electronics, I can check with them for sourcing the components.