The positive wires are connected to a positive connector within a combiner box and the negative wires are connected to the negative connector.
How to wire 2 solar panels in parallel.
The solar panels are usually designed that they can handle being backfed from one panel but if you have a whole bunch you do run the risk of ruining your solar panel.
When solar panels are wired in parallel the positive terminal from one panel is connected to the positive terminal of another panel and the negative terminals of the two panels are connected together.
If you had 4 solar panels in parallel and each was rated at 12 volts and 5 amps the entire array would be 12 volts at 20 amps.
To wire two or more solar panels and batteries in parallel simply connect the positive terminal of solar panel or battery to the positive terminal of solar panel or battery and vise versa respectively as shown in the fig below.
Wiring solar panels in a parallel circuit.