IN-12x6 V1 Tube Board Kit - $46 - Assembly instructions
6" x 1.75" | mounting holes sized for 6-32 hardware | solder pads for mounting RGB backlights
Anode 1,2,3,4 | Cathode 0 through 9, 0 through 9 | IN-12b decimal pads 1 through 6 | gnd
When using IN-12b tubes, and grounding out any of the decimal pads 1 through 6, the decimal indicators will illuminate...
...as long as one of the two GND pins go to GND on the shield, and the other goes to the desired tube's decimal pad. Note where the decimal indicator elements are. The second to the last is grounded. If your IN-12 does not have this element, it is an IN-12a not an IN-12b.