One reason you may not being getting any responses is that you have double posted your questions and that the "Technical" section you posted in deals with Forum support questions, not technical answers to your trailer. For that use "Tech Issues".
You probably won't locate a manual online. Your trailer originally came with a brochure for the trailer and a supplemental packet explaining the operation of the water heater from the heater mfg. It's all pretty straight forward--cold into water heater, hot, out to system. I have no idea what you have regarding hoses and their connections. A picture would help.
Your switch may be on the outside or may be close to the water heater, inside. You may not have one. Post the brand and model of heater for better information.