Ammeters are wired in series, voltmeters in parallel. A quick search for TVSS and circuit breaker will glean a plethora of information.
A search for "1×AC 20V Analog Panel Volt Voltage Meter Voltmeter Gauge 44L1 AC 0-20V" on eBay will connect you with one I bought. You didn't mention an ammeter, but IMHO it is no less useful than the voltmeter.