These should be pretty straightforward to print. No supports and 20% infill. For the screw holes, I like to add a support blocker (Cura) and increase the wall count to 6 to make sure these holes are solid. This prevents the screws from splitting the PLA.

I printed the SVGs to the correct size glued these onto the top of the acrylic and used this as a template to cut out and drill. This is easy for acrylic as it has a protective sheet to peel off any. Wood might leave a mess. 

Check the gallery for the wiring diagram. These meters have a weird sort of configuration with the wire colour and you need to connect a red wire to the negative side which doesn't make much sense but hopefully, the picture will help. 

The video of the project might be easier to follow.