Hi Soren,

Here's my understanding of it. Many European cars have a three-wire tail light: brake light, tail light and turnsignal. When wiring a trailer (or in my case a mismatched PV444) that has a single bulb tail light, you need something to cancel the brake light when the turn indicator is applied. Originally, in the PV444 this was done with switching circuits inside the turn signal switch. One can also use a trailer wiring converter.

You and I have the same problem. How to get the electricity in the 3-wire system to funnel into a 2-wire bulb. Here's the answer:

http://www.etrailer.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=E&Product_Code=31820&Category_Code=TB

I have no affiliation with this company. I don't even know if they are reputable. This is just an example of what we need to wire into our cars (or trailers) to solve our problem.
I found one locally for US$18. I'm sure they also have them in Denmark.

Good luck!
Hope this is clear.

Aiden
Boulder, Co
1957 PV444