For what its worth- I just thought my heater motor died and started looking for new ones. After looking over my heater, cleaning the grounds, adding dielectric grease to the connections and making sure they were all strong, it worked again **. I also had a lot of mud built up in the hoses, maybe a wasp nest in one that was completely clogged.
**Do these have a temperature switch that shuts them down at a certain temp? I have noticed mine still will work great, then shut off by itself, then after I shut the truck down, it will start back up.