O.K.
I bought a different tank to go on my savage one of the advantages is a fuel gauge, donor bike had a gauge.
Got a used sending unit and instrument cluster off ebay. Fuel gauge has two wires-- float sensor has two wires.
In my mind the float sends varying current to gauge and needle goes up and down with float position. Almost like an inline dimmer.
1Test sensor with light, wire it inline to positive side of light, other side of light to neg battery post -- light gets brighter as float rises, Good!
2 Test gauge, positve to one post- negative to other post -needle moves up, take hot wire off, needle doesn't drop but stays where it is. Reverse polarity- needle goes down, seems as though it follows positive wire. Hey but it works, Good.

Wire sensor to fuel gauge inline on positve side, ground other post , Nothing! Using the sensor I can't make the fuel gauge needle move.

Both came off same bike type, possibly diff year.

I know this can work, I'm just not sure how.
Hope my explanation doesn't confuse.
Seviersavage

you might have to invest in a repair manual of the bike for the tank.

Sorry cant do series wiring, it will light up fuel if it were to spark.
I would just say the float only puts out resistance. The BB reads it and sends out volts to the dash guage.
Cool.
Srinath.