SP2 fuel pump 3p connector question - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 6 (permalink) Old 06-26-2017, 10:27 AM Thread Starter
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SP2 fuel pump 3p connector question

At this connector, I have:
green- ground
brown- 12v as provided via relay
brown/bl- ??

What is the brown/black for? I traced it on the schematic back to the cluster. But what does it do?
I am still troubleshooting this stupid bike, and curious about this.

Thanks for the help
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post #2 of 6 (permalink) Old 06-26-2017, 10:35 AM
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the brown black wire is the fuel level thermistor. it's part of the low fuel detection circuit in the dash. essentially, the brown black is the ground for the fuel light.

when the tank is full the resistance between brown black and green is about 1200ohms, this means that the current in the circuit for the fuel light is low due to the high resistance to ground. as the fuel stops cooling the thermistor is warms up and its resistance to ground decreases. once it's warm enough (from being out of fuel), the current in the circuit increases enough to light the low fuel LED.
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post #3 of 6 (permalink) Old 06-26-2017, 10:47 AM Thread Starter
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Quote:
Originally Posted by Wibbly View Post
the brown black wire is the fuel level thermistor. it's part of the low fuel detection circuit in the dash. essentially, the brown black is the ground for the fuel light.

when the tank is full the resistance between brown black and green is about 1200ohms, this means that the current in the circuit for the fuel light is low due to the high resistance to ground. as the fuel stops cooling the thermistor is warms up and its resistance to ground decreases. once it's warm enough (from being out of fuel), the current in the circuit increases enough to light the low fuel LED.
perfect. Thank you.

I bought the bike the first week of May. I have ridden it twice- one time it stranded me. All fuel system related. I have it traced to the pump now. Just wanted to make sure I wasnt missing something.
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post #4 of 6 (permalink) Old 06-26-2017, 11:05 AM
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sounds like you got it sorted.


the thermistor is an interesting, albeit very effective circuit. the only reason i know anything about it is because i had to make my own fuel light and had a nightmare of a time lol
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post #5 of 6 (permalink) Old 06-26-2017, 11:46 AM Thread Starter
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those lights in the cluster are LED? Or incandescent?
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post #6 of 6 (permalink) Old 06-26-2017, 02:02 PM
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They're LED, but there is more to it than just putting the led in line with the thermistor. If you do that the led will light solid all the time
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