[PipKelpy]

Is there such a thing?

Trailer plug that shoves in car, instead connect it to plug which has wires attached to a 12v leisure battery, if that makes sense?

It's a hassle to keep connecting the car to trailers when they don't live in same yard. I want to be able to check that all bulbs are working without having to keep running back and forth.

Would like to see them light up to.

Any ideas?

[Q]

I saw a trailer test board years ago - standard caravan plug connected to a battery with a row of switches to test all the lights on a piece of MDF.

Is that what you mean? 

[chrismahon]

I would expect that kind of testing arrangement would be used anywhere that sold trailers or caravans. But perhaps it isn't going to be cheap and it would be best to make your own?

[Rupert the bear]

I've got one of those, idiot proof, (well it works for me) and saves faffing about

[PipKelpy]

Not to scale. Sorry about bad clarity. This was what I was wondering if possible to buy or easy to connect up for power.

[Kevm]

 Here is one I made,  just plug the trailer into it and flick the switch to test whatever circuit you want.
Handy as a 12v power supply for testing other stuff as well.
Just a lawnmower battery, a box,  some switches and a socket.

[Kiran]

Dont those plug in testers give you the same end result? Sorry I cant open the image up properly on my phone to see what you have sketched so maybe talking rubbish. But if all you are after is testing the circuits then the plug in testers work really well. You also dont need 12v as it's just a continuity test