init-system-helpers package that provides a helper tools for all init systems is not available in primary Debian Wheezy repositories. You need to use
wheezy-backports repository to install it on that operating system.
$ cat <<EOF | sudo tee /etc/apt/sources.list.d/wheezy-backports.list deb http://http.debian.net/debian wheezy-backports main EOF
Update package index.
$ sudo apt-get update
$ sudo apt-get install init-system-helpers
You do not need to explicitly specify
wheezy-backports as target release, because this package is not available in primary Debian Wheezy repositories.