What you want to do now is find out what voltage is required from the sending unit to trigger the low fuel light to come on. Lower the float until the reading on your voltmeter is 2.0 volts. Place a screwdriver or some other object under the float so the voltage will stay at 2.0 volts and let it sit there a minute. Then slowly lower the float bit by bit until the low fuel light comes on. This is a bit of trial and error but very important if you want to get it right. On my bike I discovered that the low fuel light would come on when the voltage was at 2.3 volts but it doesn’t come on instantly upon reading 2.3 volts. It takes a little while, maybe 30-60 seconds. I would suggest you find the voltage that will cause the low fuel light to come on then turn the ignition off and then back on again. If the low fuel light is now off, let it sit a couple of minutes with the ignition on. If it still remains off, you need to lower it just a tad and let it sit for a minute or so, keep doing this until the light comes on.
Once you know the accurate voltage that will cause the low fuel light to go on, it is a simple matter of bending the rod that is attached to the float so that the voltage reading that will cause the low fuel light to come on, wont read that voltage until the float is resting about 3/16 of an inch above the black fuel pump assembly seal. The reason you want that 3/16 inch gap between the seal and the float is to compensate for the thickness of the tank which has a raised lip where the fuel pump assembly mates to the tank. If you fail to take this gap into account, you might have a low fuel light that will never come on. Take a look at the below picture, as the unit comes from the factory the float rod is straight as can be. As you can see in the picture my recalibrated rod is just slightly bent. A little bit of bending goes a long way in adjusting the sending units voltage output.
Once you have made your adjustment disconnect the four wire connector from the bottom of the fuel pump assembly and reconnect the electrical 2 wire connector for the fuel pump. Remove the old fuel pump assembly seal and install the new one. Once again a word of caution, when you go to install the pump assembly into the tank be careful with the fuel level float. You have to turn the assembly at an angle then gently force the float into the tank. Also notice that the fuel pump assembly angles off to one side, if you try to stick it in going down the center of the tank you are going to break something expensive.
Once you have the assembly in the tank put the 9 washers on the 9 studs followed by the 9 nuts. Tighten down the 9 nuts using a torque wrench set at 5 NM using a crisscross pattern. Now remount the tank on the bike and install the fuel hose using the 2 new aluminum crush washers. Torque the banjo bolt to 15 NM using a 18mm socket. If you don’t have a 18mm socket a ¾ inch socket will do. Reconnect the 4 wire connector on the bottom of the fuel pump assembly. Reconect the two thin hoses to the bottom of the tank and bolt the hose bracket to the tank. Lower the fuel tank and bolt it down. Reinstall the 20 amp headlight fuse. If the tank was completely emptied add 1 gallon of gas so when you turn the ignition on the fuel pump isn’t running without fuel.
Now the moment of truth, turn the ignition on, hopefully the low fuel light is on. If it isn’t let the bike sit a minute or so with the ignition on. If it still isn’t coming on you got a problem. Your choice is to take it all apart again and start over or you might be able to stick something through the filler neck and bend the float slightly up.
Update.
I just went through my first full tank of fuel since doing the recalibration and these are the results.
The low fuel light came on at 166 miles. And it took 4.53 gallons to fill the tank back up. With this tank of fuel I got 36.6 miles per US gallon, which was mostly highway miles doing 65 to 75 mph. If I got 36.6 mpg and if there was 1.47 of usable fuel still left in the tank, that means I could go another 53.8 miles before I would run out of gas.
My goal was to recalibrate the low fuel light/gas gage sending unit so I would have 35-40 miles worth of gas in the tank when the low fuel light came on. So it appears that the best I could do was almost 14 miles more than my goal. Oh well, I can live with it. It is certainly better than the 90+ miles that is left in the tank, as the thing comes set from the factory. It is my belief that this is about as well as the sending unit can be recalibrated and still have a low fuel light, that works. The problem is that the fuel level float bottoms out on the tank belly while there is still quite a bit of fuel still left in the tank and there is no way of making the float sink lower as the remaining fuel level decreases. Overall I am very pleased with the results of the recalibration.
For those of you who have a fuel gage on your bike, like I do, you may be interested to know that the fuel gage works much better now that I have recalibrated the sending unit. Prior to the recalibration, at about 90 miles the fuel gage would read ¼ full. Here are the results after the recalibration. The fuel gage now stays pegged at full for the first 30 miles. At 66 miles the fuel gage reads ¾ full. At 96 miles it reads ½ full. At 125 miles the fuel gage reads ¼ full. And at 166 miles the gage read empty just as the low fuel light comes on.
I hope my efforts help everyone who has been frustrated by this problem that Triumph has so far, not been willing to address. Hopefully they have cured this problem on their new touring model that comes with a fuel gage from the factory, standard.