Hi 2old boy,
The marker lights on your Carioca ci 625, will be part of the motorhome conversion, and not the Fiat base vehicle. It is therfore more probable that you will obtain a specific response from a dedicated MH forum.
You vehicle will possibly be corstructed from a Fiat chassis cab, with an Alko or similar? rear chassis attached. A possible routing for your marker light wiring would be via a junction box on the chassis, where the connection to the Fiat wiring could be made. A lack of adequate cable support in this area can cause problems with broken wires.
This forum is the place to seek help with Fiat base vehicle problems. Please note for future reference that 2006 was a Fiat Ducato model change year. The earlier x244 models with roughly rectangular headlights were phased out and replaced by the x250 models with more slanting headlamps. Engines and other components were also changed.
Please check your base vehicle model from the VIN (xxx244nnn......, or xxx250nnn.....). Also engine eg 2.8 jtd, or 2.3 multijet.