Goofy temp gauge

[dropnstylez]

Dont know if this should be here or elec. but here it goes, 77 350 c10 temp gauge goes up about to about 1/8 on the gauge. I can ground the wire from the sending unit and it pegs it hot like it should, whats my next move? i dont know how to test sending unit or gauge? and trying to clean connector i kinda broke the brittle "connector" anywhere in particular to pick up a new one? it still hooks on but has a broken corner and i dont like it being brittle if im going to be replacing other stuff on it..

thanks in advance