Trailer lights wiring hook up

[sugarman]

Hi,
I have a 2004 S80 and I had a hitch installed to pull misc small type trailers but I didn't not have the lights hooked because I was told to be careful and have the wiring hooked up on a separate circuit so as to protect the car's computer. I was a bit worried when I heard this at the towing store so I thought I would do a bit of research and see what the proper way to hook up trailer lights which is the easiest and safest as these guys might not be familiar with Volvo electrical. I will be using trailers that have the standard 4 pin plug.
Anyone with experience please let me know what you used for a wiring connector/harness and where is the best place to purchase (online).
Thanks,
Andrew