I did this job recently but it took a long time because I was unable to get any info from FIAT UK or dealers etc. The mechanical fitting side was dead easy but the wiring took forever to figure out. I eventually did it the hard way by delving into the very restricted space behind the jack and stripping back some of the harness to expose the cables. From there you have to use a 12v probe to identify the live wires one by one as you operate the varoius lights. One tip which I have just discoved some weeks later is that there is a blanking grommet in the rear wheelarch behind the n/s wheel. If you remove the interior trim panel beneath the jack, this grommet is clearly exposed and you can then neatly feed the towbar cable through into the interior at the point where the wiring loom is accessible.
(Better still let the pros do it for you!)