If your car has a 13 pin electrics plug but your caravan or trailer has a 7 pin electrics plug, then you will need a 13 pin to 7 pin adapter. This would be suitable for towing a bike rack or standard trailer or you would need a 13 pin to twin socket adapter to tow an older caravan with twin electrics.

What is the difference between GREY and Red Anderson plug?

By using red Anderson plugs you are protecting your system from being hooked up incorrectly. Likewise, if you are using a panel with a regulator already fitted then you would have a grey Anderson plug (after the regulator) as it is safe for direct connection to a battery.