I have used Towequipe several times - their kit is good value and comes with very good instruction sheets; they have an excelent customer service hotline too in case you get in difficulty.
Also a very good website is Ryder towing, you don't have to buy their relays but their Adobe downloads are great and include a very informative general info description on all things towing electrical which will certainly answer all your questions.
Hope this helps - havn't given the links but both sites are easy to find on Google.
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