rwise,
I do not know how the gauge unit is grounded to the gauge housing on the '49.
The housing itself is grounded to the body by the nut/bolt/screw that holds it to the dash (the dash should be grounded). You could check this ground with a continuity test between the housing and any other clean/bare metal on the body/chassis.
If the gauge unit does not need to be grounded, let's hope that someone corrects me.
Tim
