You'll need p/n 75049-01A



long orange wire = power and runs to harness

long black wire = ground and runs to harness

short yellow/white wire = signal and runs to floater

short black wire = ground and runs to floater

 

I'm not sure what a p/n 75049-01A is, it looks like the number on the gauge pictured above is 75049-01A. For what it's worth the number on on my 08 FB gauge is 75053-01.

I've jibber jawed about this long enough w/o knowing for sure, so I went to the garage and pulled my fuel gauge out for a bench test.

The 4 position plug for my 3 wire gauge is located below my tank...



So I dis-assembled the plug & pulled the gauge...



Positive DC current flows through the gauge via the orange wire then through the variable resistor located on the sending unit through the yellow wire, then to ground through the black wire. The sending unit float controls the amount of resistance in the circuit.
If there is little resistance to ground through the yellow wire the needle will sweep to the 'full' position.

I applied +DC voltage to the orange wire and grounded the yellow wire in accordance with the test prescribed in the electrical service manual. The gauge indicated 'full'... which means my gauge is functioning properly.



So... it seems to me that a 3 wire gauge could be neatly wired into a ‘4’ wire application something like this…

 

To 08:

Good write-up, 08!

75049-01A is the p/n for the fuel gauge used on the 1999-2003 WG and FXDL tanks (see images below).

As you will notice, the fuel sending unit and fuel gauge are at the same hole in the tank. That's why these Dyna models have only two long wires running from the fuel gauge through the tank towards the harness. The two short wires (B and Y/W) run directly to the fuel sending unit underneath fuel gauge.
Here's an overview of the FXDWG & FXDL parts (1999-2003 models).

2004 and up FXDWG models have the fuel sending unit under the central console. That's why three (O,B,Y or Y/W) long wires run from the fuel gauge through the tank and connect to the harness under the tank. From there the Y or Y/W wire from the gauge connects to the Y/W wire at the fuel sending unit.



Question to the OP:

What year is the FXDWG tank you bought?

Could you post some images from tank, sending unit and fuel gauges?

To 08:
I second your opinion.

Assuming OP has an FXDWG tank were the sending unit is under the central console, he has to run an extra (Y) wire from the gauge to the sending unit though!

 

I have to replace the bulb on the indicator fuel level ... is it possible?

 

Just wanted to say Thanks for making my day easier !!! ,, needed a wiring diagram to mount a FXDS tank , with on board fuel gauge (1998) to a 1988 sportster 1200 !!!,, I really wanted a gas gauge !!!

 

how did you wire it up on the sporty???