Gas tank swap.. electrical question
 

I just swapped my 84 GS gas tank into my 83 GSL. I did this because the 83 tank was rusted out. I failed to notice that the 84's fuel guage sending unit connector has three wires and the 83 was only 2 wire. I know that the black wire is ground and the yellow wire is the hot to the guage. What do I do with the blue/yellow wire that ran to the 84's instrument cluster. I omitted it completely and the guage doesn't work.. Do I need to splice the yellow with the blue/yellow? Or am I out of luck.. Thanks in advance for your help.

i think the 3rd wire should be the low fuel light. its fine to leave it disconnected. try connecting the gauge to that wire instead maybe you them reversed.