Faulty tachometer

[johnlangford]

Recently bought Yamaha ybr125 custom 2008. - runs well
But rev counter not working.
Inside tachometer two wires blue and black for light then three wires
Black
Green
Black/ yellow
I see 6.3 volts between b/y and ground with engine running but no voltage on green!?
Does this mean fault is probably in ecu?

[Nobby the Bastard]

Normally you would expect an earth, a reference which will be whatever you measure across the battery, and the signal which will be somewhere between 0 and the reference voltage which will depend on engine speed.

Seems your ref voltage is missing. I would try connecting the green to the positive connection on the battery when the engine is running.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[WD Forte]

The manual shows the tacho has 3 wires if we ignore the back light
Power in (12v) on a Brown wire
This also powers the fuel gauge,eml and neutral lights

Ground on a Black cable
this ground is also common to other lamps and gauges

The tacho gets its driving pulses from the ECU on a Black/Yellow cable
when the engine is running.
If you cant detect pulses on this when the engine is running, you wont get any movement
on the tacho.
At this point we dont know if you have a steady 6.3 V DC or your meter cant handle
pulses and is averaging out what it reads

The only green cable I see in the area is the cable between the fuel gauge and sender so you may be a wee bit confused?

I may be of course, but I doubt it's the ecu or tacho at fault
its an old bike so I would check and clean all connectors first
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bikers smell of wee

[jeffyjeff]