fuel gauge not workin

[BigRedJeep]

last week my gauge went from 3/4 to over full drivin down the road. i grounded a yellow wire with white stripe, and the gauge went to all the way empty. is the sending unit bad or is there a trik to fix this.? sux because i dont know how much fuel i have. milage changes with a trailer and without.
thanks

 

[JLDickmon]

I'd almost have to say sender unit, cause when you grounded the wire the gauge itself responded...

make sure it's getting it's reference voltage