I am in the US and your question explains some of the differences in what we are saying. Our trailer lights are different.

Many years ago cars in the US all had the same setup for tail lights They had two filaments or bulbs, one for tail light and one for Stoplight
in the 30s and some of the 40s turn signals were a option and were added to the Stop light. The same filament served for Stop and Turn signal.

After turn signals became standard the wiring stayed the same.

Our small trailers are wired with 4 wires. Ground, Tail, Left stop/turn, and Right stop/turn.

My 1969 BMW was the first car I had to install a adapter in. I built my own using relays. I have had to put one in every car since then.

Now many (perhaps all) US cars use separate bulbs but the trailer lighting hasn't changed.

When I bought the CX-5 I decided to get the factory wiring. They handed me the kit and as soon as I opened the box I realized that the two pins to add to two connectors and the instructions were Mazda stock, the modal was a commercial off the shelf adapter with a Mazda label stuck on it. I installed it anyway because I don't have a problem with tapping into wires.

We still differ in that I don't see any way to blow up anything or set a fire back there.

 

The one job that sticks in my mind was a 2004 or 2005 Mazda 6. The BCM was melted and so were the wiring plugs from the dash loom going into it. It was investigated by Mazda New Zealand & was atributed to non genuine trailer wioring. The customer was towing a trailer at the time of the incident. The interior of the car smelt of burnt plastic. We had to replace the entire dash loom & BCM. Luckily for him no other damage was done.

Also in BT50's there is more & more cases of module corruption due to, in most cases incorrect wiring of accessories into various circuits. Modern cars have very high tech & sensitive electronics & it doesn't take much to upset them.

 

This is why I recommend the powered modals, either from Mazda or from Etrailer In the powered unit, the cars wiring provides a signal to the modal. There is no electrical connection from the tail lights to the trailer and no load on the car lights.

The trailer lights have there own separate power and fuse.

Quality parts and quality work are important. Both can be obtained from a number of sources.

Frank