trailer hook up wiring

Some time ago I remember reading here about cautions re: correct factory wiring for trailer hook ups. As I recall there was a relay necessary to pevent burning up headlight switch. I have a '97 3500/cummins. I
discovered the truck did not have the factory towing package. Having just replaced the headlight switch. I would like to not repeat the effort. Can someone refresh my memory with respect to trailer wiring. I would like to go with a 7 pin rv pigtail. I stopped at my local dealership for help. I was greeted with a blank look. Not the level of help I expected from a professional. Thanks in advance.
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Joe Fishback wrote:

http://www.dodgeram.org/tech/mods/electric/trailer_wire.htm
--
Ken



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