There is no plug for the 12S circuit there is only a Plug for the 12N circuit
3 Options
1) Buy the pucker LR Kit for the main stealers which has the Loom Socket and relays and plugs into the fuse box.
2) Buy an aftermarket kit - have a look at towsure
3) Make your own system up
I did the latter as a) I had all the bits already b) I Can c) it is a lot higher spec than a bought kit