Ensure no pieces are broken or stuck in the connectors before use.
The Branch connectors should have the same voltage passing through them as the panels themselves. Place the leads of a multi meter across both pins of the panel. Note the pins of the meter must make contact with the metal pins of the panel to obtain a correct measurement.
You should see between 20-15 volts depending on sun conditions. If this number is lower then there is an issue with the connection with the meter or an issue with the panel output.
The same measurement can be completed for amperage. Note: make sure your meter is able to handle the rated amperage of each panel.
Solar panels from 10 to 100 watt panels will require a 5 amp meter. 190 watt panels will require a 10 amp fused meter.
Change your meter to the amperage setting and complete the measurement in the same manner.
100 watt panels should register at around 5 amps. Current of 190 watt panels can be up to 9.3 amps, depending on sun conditions. Multiple panels should all have similar numbers if they have the same sun conditions.