where is the other end of our dash's ground?

i mean one end of the ground wire connects to our gauges where does the other end go?

chassis or engine block behind the cylinder/valve cover on the driver side???

i'm only asking because my gauges don't seem to be giving me teh right readings

they are aftermartket digital gauges and were fine but i just want to rule out a bad ground before i look eleswhere

everyrthign was working fine for months and now im reading 30 degrees higher than usual and im dont think its right.

my tach is slightly quirky at times meaning it will read fine but occasionally display some weird number or ----- for like a blink of an eye and then go back to normal operation

my oil pressure reads -1 to -3 with just ignition on when i already calibrated it to read zero before starting the car


just want to rule out a bad ground and i need to know where the gauges get there ground

thanks