This is my way of putting a Voltmeter/Ampemeter between my solar panels and the MPTT controller (pending installation of both in a plastic box).
It is no big a build, but I am posting it to explain the proper wiring of.
The solar MPPT board and the V/A-meter parts.
The meter measures current by being inline with the NEGATIVE wire. Do not be perplexed by the red/black colors (no. 1) to the big connector.
Naturally in this case to the positive wire (no. 2) is left untouched.
Voltage measured is done by the thin red (no. 4) and yellow (no. 3) wires, when the meter sees enough voltage to power itself.
If you are to power the meter by another source, then you connect the thin red/black wires to the source and the yellow inline with the Positive Out.
And here is a pic of the suggested wiring by a seller.
YES, it is counterintuitive, but both the thin yellow and the red wires are connected on the positive lead, on the output and input jack respectively.
And this is the back side of the meter. Current is measured on a build in wire shunt.
Hope it was of help…