Scales use electronics with negative power supply. Using them without modification will cause many troubles, because of necessity to isolate metal body of the scale/caliper from the system ground. Better modify them to have their bodies connected to the ground of all system. The scales are slightly different, so use the following as a guide and modify instructions according to your scales.
1. Unscrew and remove bottom part of the caliper
2. Unscrew and detach PCB
3. Remove foil at the edges of PCB holes (with drill bit) of the screws removed at the 1 step. The idea is to prevent touching the screws of the PCB ground (normally connected to the + of the battery). Only edges, do not make holes larger!
4. Make a cut at the right-bottom hole to detach this hole from the ground and connect this hole to the minus instead (I also solder thin wire to be sure that screw will be connected to the minus). The corresponding screw is the only screw with thin thread. Grounding the body to the system ground is made through this screw only.
5. If you are going to use connectors, cut connector (mouser.com part number 798-DF3Z-4P-2H20, manufacturer part number DF3Z-4P-2H(20) to rectangular shape (with knife) and make corresponding hole in the plastic body of the caliper (with knife). Alternatively you can solder wires directly to PCB.
6. Put PCB back, use small screws (removed at 2) to attached PCB to place. Cover these small screws with thin tape.
7. Attach back the part removed at 1.
8. Check carefully with Ohmmeter: The left pin (top image) must have connection to the metal body of the caliper. The other pins - not. The right pin must have connection to the plus terminal of the battery. Batteries are not needed for DRO system, since the calipers are powered from USB or serial, but you can check normal operation of the sale after modification by inserting the battery.