Lights issue with a trailer

Last night we collected a trailer, the first one I've towed with the recently wired in towbar.
All wiring was done as per the available instructions but last night we hit a snag.
It was only a 20min drive to get home and about 10mins in the ABS light came on. Then a few mins from home the dash lights went off. I stopped and found both the trailer and Jimny rear lights off, though the indicators and headlights still worked (never thought to check the brakes).

Once home and the trailer disconnected the ABS light went out, but the rear lights remained off on the Jimny.
Clearly a fuse has gone, but the question is why?

It's a 56 plate Jimny, with a Towtrust towbar and wiring spliced into the loom behind the rear left trim panel (soldered joints).

Any thoughts or suggestions?

short on trailor harness ?

would explain why ABS went off after trailor disconnected

replace fuse and check if rear lights OK

then re-attach trailor and see what happens (was it wet, could it have taken 10 mins to soak through and cause issues)

Do you know/ have anything else to test in it?

Tip:

Don't fiddle with the trailer bulbs when the plug is in and the lights are on on the car, even though it is the obvious way to find the fault, it just blows fuses.

(I did it to my Nissan*, and blew the tail light fuse, which on a Nissan is a secret special fuse that they don't tell you about, and to replace it half the car has to come apart, as it is buried in the Intelligent power distribution module. I can honestly say that I have never seen such a stupid design in my entire life before )

* What I actually did was take the cover off the light to wobble the suspect bulb. All the bulbs clip into an earth plate, held in by the cover. Without the cover the plate moved out enough for the spring contact to slip off the pip on the bulb to the side case of the bulb and blow the fuse.

Took half an hour to change that fuse.

Thanks for the quick replies guys, much appreciated.

Halford, was it wet? Oh yes! A reet downpour.
That might help to explain why it took around 10mins for a fault to show up.

Daniel, my knowledge is quite limited, and my equipment extends to a multimeter.
I can always have my Dad on the phone, he was a sparky many moons ago, but still knows how to keep the magic smoke inside the wires.

If the rain stops (might be abandoning the Jimny for our kayak....) I'll get out and hopefully get the Jimny sorted out. That's my priority at the moment, the trailer can wait, but rather than trying to chase a fault I think I may strip out all the existing wiring runs to save wasting time chasing potential faults. The trailer was a steal anyway, so I don't begrudge spending money on it right away.

Cheers guys.

I don't know if you could spray anything in both parts to disperse the water?

I'm not a mechanic or sparky sorry just throwing some ideas about

What condition is the trailers plug(female connector) in? They can corrode terribly as they spend most of their life disconnected and normally open to the elements. You can get replacements in ali (I have a few of them of which you could have one for postage costs) or the normal standard plastic.

I haven't had a close look at the condition of the plug on the trailer, but there's a dummy socket on the trailer that the plug's parked in when not in use.
It points upwards so water may be able to accumulate in therr.
Definitely something to check over the weekend.

Thanks for the offer of the ally terminals, I'll let you know.

Hi, when you spliced the wiring did you earth the white wire on pin 3?

I don't have the wiring diagram to hand but was the white on the plug to the black in the Jimny loom? That's me applying a non-sparky's logic that black = earth.....

Ok, ai think I'm going mad. Where on earth is the second fuse box??? The manual says under a panel on the underside of the dashboard on the drivers side. I've looked, there's no removeable panel, just the dash and he underside of the steering column shroud. All I can see are connectors and loom behind the dash, and all I can see on the passenger side is the ECU.

HELP!

Looks like this on my 07 plate