You said that the caravan electrics work ok, how are you testing them?
Are you using 7 pin or 13 pin plugs? If it's 13 pin are the pins correctly aligned? I wonder if it's possible to connect a 13 pin plug with the pins turned slightly so they do not align with the correct part of the car socket.
If you mean that with caravan hooked up to car the caravan road lights are not working & car side of things has been checked ok then first thing to check is caravan plug that plugs into towbar socket. Dismantle plug & check connections & go from there.
If you cannot fix it yourself then any caravan workshop will fix it.
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