Just take the + signal behind the ignition to make sure the gauge doesn't stays on all the time.

I used this voltgauge:

https://de.aliexpress.com/item/32953332461.html?gatewayAdapt=glo2deu

I used M3 x 5,7mm fusible threads on Part 1 to connect the two parts.

Notes:

Position the parts as they will be mounted later.

Part 2: Use supports only on this part and make sure that support roof is activated to ensure a good surface on the curve and easy removal of the support.

Even if there is not a big load on the component, I recommend printing with PLA+ or better PETG to counteract effects from the sun.