I have a keystone 5er and tried to find the same information that you are looking for with absolutely no luck. I resorted to pulling off the cable wall plates and removing the stereo to figure out what cables go where. If you join the keystonerv.org site which is similar to this site someone could probably provide you info with regards to your exact trailer.
2008 Silverado 2500HD, Z71 off-road, Z85 towing
2005 Keystone Hornet 245RKS 5th Wheel