mine had em as standard so prob best to copy how ford did it
my 57 plate had a ford fitted kit but was done at the dealer off the existing wiring on a van ordered without rear sensors (dealer fuck up) they also cut the holes badly so 1 sensor rotated and went off cos it thought a post was comin up when it was the ground
my new van had em done much better
you want the beeper/box to be as close to the cab and you can tho so you can hear it, i cant hear mine over the stereo sometimes and its in the cab somewhere