Gas/oil press gauge inop

Rally dash the IVR is inside the fuel gauge. You will have to bend the contact open / RTV it to disable that and make sure there is no wiring in there than can screw things up, then "hack" an IVR in from the outside. The fuel gauge has three terminals. One is the sender, one was 12V IN to the IVR, and the remaining was the IVR output which jumpered to the other two gauges.

As Rusty said check connections. And add a ground pigtail from the cluster to the dash frame.

Check the PC board harness connector pins. You may have to solder them to the board traces