Hi Robbo77
You can connect the radio straight up without changing anything (pin 7 goes to pin 7 and pin 4 goes to pin 4) and the radio will work for testing the unit. It will drain the battery and not remember the programming so its not to be left like this. Its only to see what still works.
Swapping the pin 4 and pin 7 on the power plug over puts the stereo power back under computer control to save draining the car battery and then shutting down the central locking and alarm system..........
Not knowing which adaptor you have (as some are generic ISO and some are specific to the Citroen C3) I can't say what colour the wires are, or if they need changing.
If you have a generic ISO connector on one end and a Kenwood plug on the other, try swapping over the wire that goes to pin 4 on the ISO plug with the one that goes to pin 7 on the ISO plug (and vice-versa).
Colours would probably be yellow and red, but you must identify the wires by the pin number!
there is a picture of the ISO connectors and their numbers here:
https://pinoutsguide.com/CarAudio/car_au ... nout.shtml
the fuses in the glovebox guide is here:
https://citroenc3owners.com/citroen-c3-t ... -t153.html