Help with an ammeter for a box

[Pearls not a Singer]

The induction type were fitted to Rubies and are far safer as there is less risk of a detached wire causing a short.

Joining  the ends of the existing wires provides a  good opportunity to insert a 20amp inline fuse into the circuit.

Before you fit it to the car, either experiment with a jury rig or find a reliable source for the correct orientation of the loop so that charge/discharge are on the correct scale

Hope this helps