depends how you checked continuity,
i'm not sure i understand what you explain. so just to be on the safe side
if you have a beep tester on your meter do the following
put red to the gauge/instrument cluster case and black lead to one of the studs. if it beeps you have a problem
if it doesn't beep all good
check the other stud
if you just set the gauge to resistance/ohms
between case and a stud you should have infinite resistance tyr it on all settings
if you measure some resistance a few ohms or even a few Kohms or Zero resistance you have a problem. the lead connected to the stud can "see" the lead connected to the caseing BAD....!
basically no electricty should be able to flow from one of those studs into the caseing,
if it can flow that would indicate a dead short.....
Dave