1993 750SS. I working my way through a number of issues with my fuel tank one of which is the fuel sensor not working. It seems to sensor itself was faulty due to frayed wires near where it enters the underside of the tank and instead of replacing the item it would appear the previous owner cut the wires entirely. I suspect this was because the sensor was painted into the tank on the inside - not ideal. I have managed to remove the sensor and fit a new but I am trying to work out which wire does what. The new sensor looks like this with 4 individual wires: Sensor black -> fuel sensor (assuming negative - ?) white -> fuel sensor (assuming positive + ?) black -> fuel pump negative - red -> fuel pump positive + Over on the bike the previous owner has left me with this (was a little tidier before I cut back the heat-shrink): Bike blue -> ? brown -> ? black -> fuel pump negative - red -> fuel pump positive + I have bought a connector kit and crimp to tool to terminate those wires and to mate with the new fuel sensor but I am a little unsure on which wire fuel sensor wire goes to which. Help! bike -> sensor blue -> ? brown -> ? Looking in the Haynes Manual I my thinking has brought be to the conclusion: bike -> sensor blue -> white brown -> black My questions: Does it actually matter? Am I right? bike -> sensor blue -> ? brown -> ?
you are correct - it's vital that red and black are connected/orientated correctly for fuel pump but remaining two wires are both isolated from either pole and so can be wired either way round of the two alternatives.
Getting the poles correctly orientated is vital The other two are basically switch wires, there to make and break the circuit.
New fuel sensor fitted. New fuel tap. Tank flushed out. New fuel filter fitted. Replaced a few of the hoses inside. New jubilee clips. Terminated the wires from my bike for the fuel pump and sensor with correct automotive connector. Refitted and correctly oriented my fuel filler cap, new seals. Put a splash of fuel in the tank and rode around the block. All seemed well and the low fuel light was on. Filled the tank but still the low fuel light is on I doubt the sensor will be faulty but it is the only thing I can think at this moment. Stuck float in the sensor perhaps or shorted wires when I made my connector?
The sensor in the photo doesn't look like a standard SS one although that doesn't mean it is incompatible. Some sensors work with a float that rises and falls to switch on the warning light and some use a thermistor and have no moving parts. I don't know what system yours uses but, with the sensor in your hand, you might be able to feel or hear the float moving inside if it has one. There is a thread in the Supersport section where I changed mine here. https://www.ducatiforum.co.uk/threads/fuel-level-sensor-1994-600ss.83332/
The new one is a Ducati part, it is plastic and I think has float inside where as the old was made from metal and has a thermistor inside. I think Ducati have learned overtime and improved / simplified the part. You link is interesting as it links to this page: https://bradthebikeboy.blogspot.com/2020/06/playing-with-ducati-fuel-level-sender.html I will see if I can test the wiring on both sides of tank in situ and failing that drain the tank and remove the sensor. I am hoping I will have enough length on the fuel pump wires that I do not need to disconnect them (which means removing the fuel filler cap, fuel filler, and other pieces inside the tank first!).
Looks like the new sensor in your photo is a plastic one with a thermistor, don’t think the SS sensors ever had floats in them TBH. They were notoriously unreliable, so was you replacement new from Ducati or second hand? Also worth noting is that the originals came with a plastic nut which was prone to cracking when fitting to specified torque. Ally nuts were available as aftermarket items but you need to remove the electrical connector to replace, but later sensors may have come with metal nut.
The new is a Ducati replacement part direct from them. So we think that is a thermistor too. Interesting. I have a metal nut from the sensor I have just removed, it is large and fits the sensor into the tank.
Following image from an internet search suggests there is a float in the black plastic units after all, so some form of variable capacitance device. That said if you purchased a new replacement from Ducati then highly unlikely to be the sensor. The poster said fuel light on all the time so replaced the sensor and cut the original part up to see how it worked, but following replacement with new, the fuel light still remains on all the time. When asked what finally fixed it response was 'Don't know, the light is still on all the time....' Not very helpful I know...
The sensor I removed: The new replacement, very similar to the photos in the previous post yes: I'll take a look at the wiring this weekend.
I have removed the sensor and had a closer look. It is a float type. I could see 2 holes at the top for fuel to pass in / out but much like in the link the hole at the bottom of the sensor was closed so fuel could not leave. It seemed like the float could potentially get locked if there was air trapped beneath it. https://bradthebikeboy.blogspot.com/2020/06/playing-with-ducati-fuel-level-sender.html I have drilled the lower hole out and now I can blow through the lower hole and air passes through the chamber out the top. When I put the voltmeter across the wires I was reading 4.5 ohms with the float at the top and 3 ohms with the float at the bottom - not quite what I was expecting. I was expecting it to behave like a switch, on / off depending on the float position. That would be how the bulb on the dash work, on / off. Now if like in the image above, the sensor contains a circuit board with some capacitors, then the orientation of the 2 wires could matter. I might swap the wires around. That is the only last option to me.
