Many pictures here...

http://www.kfzderwehrmacht.de/Homepage_english/Trailers/trailers.html

http://www.kfzderwehrmacht.de/Homepage_english/Trailers/Heeresfahrzeuge/heeresfahrzeuge.html

essentially the Hät wagons are the HF1(two horses) and HF2(heavy four horse) both saw service for a considerable time(pre Ww1 onwards) with only minor alterations..
I have a pic somewhere of the HF1(although the designation is different)being used as a radio wagon in WW1.. search light were sometimes carried on wagons even in WW1 as well and of course generators, balloon wagons etc...

Cheers