My manual says that light electric is for trailer up to 10,000, heavy electric is for trailers over 10,000 pounds. The hydralic light and heavy read the same.
As I remember when messing with the light and heavy electric settings all it seemed to do was change the gain. If I choose light I think it set the gain at 2 or 3, heavy set the gain at 5ish. I kind of think the truck remembers where you left the gain for each of the four settings so if you tow a light trailer and use a gain of 4 then tow a heavy with a gain of say 7 all you have to do is switch from light to heavy electric and your truck will remember what gain you like.
I couldn't tell you if I have mine set on heavy or light but I do know my gain is set on 6 to 6.5 for freeway driving and I set it to 5 when driving the city streets. I like to have my brakes set tight when cruising down the road.
2015 Eclipse Iconic Toy Hauler made by Eclipse Manufacturing which is a pile of junk. If you want to know more just ask and I'll tell you about cracked frames, loose tin, walls falling off, bad holding tanks and very poor customer service.