how does it ground ??

1712712091469.png

On my '67 its a wire with two ring terminals the other end going to the radio supportscew where it mounts to the dash.
1712712317271.png

IVR on the Rally panel grounds as shown here
https://www.forabodiesonly.com/mopar/threads/gauge-cluster-issues-ivr.455893/post-1972855400