I have a horse trailer that I tow about in the dark at times. I would like to add some lights that light up the inside of the trailer, using led work lights I reckon.

But I'm not really sure of what the current ratings of the side light circuits are that the freelander provides to the trailer Does anyone know?

Think I could help you. (look at my profile)
Can you tell me exactly the extra wattage of lamps you are going to add? Another member of the failed FL2 clutch/DMF club, twice.

The trailer has its 5w tail lights and a forward facing white light (5w) on each wheel arch. It also has a puny 5w inside light , but I don't know which side it runs off.

I was thinking of a pair of lights on eBay that seem to advertise as being about 27w or so. Ideally I would like to fit 4, but 2 would be ok.

The sidelamp circuit is protected by FET's within the CJB. There are no conventional fuses.
You'd be at risk of damaging the CJB and more than likely the smart FET's would shut down.

Even with conventional fuses, you'd affect the volt drop of the sidelamp circuit let alone the problem of fuse values.

Sorry, but deffo not recommended  Another member of the failed FL2 clutch/DMF club, twice.

The only way to get the supply you need is to have a 12S socket fitted to the car and wire up your interior light to Pins 3 and 4.this should not be too expensive (done by a local independent auto electrician)and could be useful if you ever need to tow a caravan.
Or indeed if you take up caravanning to annoy Chicken George.

I think Pegleg would agree that this is the only safe way to go.

Bill. Life Honorary Member of Wallasey Motor Club.
Licenced MSA Radio Operator for 35+ years.
Rallying is the only sport.

"The sidelamp circuit of the car is protected by FET's" but that circuit has nothing to do with the 7 pin trailer socket power wise.
His 7 pin (N) would either be fed direct from the trailer module or via a bypass relay.
Either way the cable size is adequate, and a point to note is caravans have extra 'marker lights' in addition to the sidelights so I would say it would be OK if LED's are used.

I do actually have the second socket wired in at the tow bar . I was wondering whether it could be done simply off the single 7 pin.

I've never used the second of twin electrics, so I'll do some reading up about it.

Oops. Forgot about the trailer module
Have you seen a schematic of the unit Dave? Another member of the failed FL2 clutch/DMF club, twice.