What happens when an ammeter is connected in parallel?

It would be equivalent to adding a high value resistor (>10M ohms) in series in the circuit. Voltmeters typically present a high internal impedance so as to not change the current flow in the circuit you are tying to measure.

the circuit wont work the voltmeter only takes a voltage reading power does not actually pass through the meter

sometimes it can be used to measure very low leakage current using the hi impedance of the meter. EXAMPLE leakage offset from an amplifier. it could be into the nanoamps.