Location relay e320 cooling fan relay location

Go to the dealer and ask to look at their manual for this model.
You can buy the official electrical manual for this on ebay... get the real GM paper one. Stay away from the disks... they are usually bootleg and very lacking in information.
Subscribe to Mitchel, Alldata, or some other service for your car. They have good data and schematics you can print.
DONT LOOK AT HAYNES MANUALS... when it comes to electrical, they suck. Go find a factory copy or get a data sheet printed or copied from a pro manual or from the real service manual.
Print out the entire power distribution part of the schematics. This is where most problems are and the most valuable part of the electrical diagrams.
Make sure you have a good Digital Multimeter and a good test light like Dorman LED test light that shows polarity and voltage from Autozone or Advance about $20