Welcome to the forum Richie, you will find once you have the C5 alive wiring kit on and a good battery its the best way to keep your C5 easily on the road, I had problems trying to use the original key switch (difficult to keep a good connection all the time)
P.S They are easy to fit and come with instructions a fool can follow (I did) and you can keep the old key switch and wiring for if you ever decide to refit them.
Retro Andy.