￼￼Here is a link to the Suburban manual: http://www.dyersonline.com/downloadf...tfile_id/1984/
It has 2 separate wiring diagrams on pg. 4….one for the 120VAC side and another for the 12VDC side. There is no relay in use for the 120VAC, and you can easily use a common 15amp 120VAC wall switch to activate the 120VAC going into the water heater. On the front of the unit, you will find an on/off switch in the lower left corner which is a service switch for the 120VAC. There is also a small metal access that reveals the 2 thermostats.
The wiring for the igniter (module) board is simple and straight forward….even color coded. These wires lead to a switch plate supplied with every unit by Suburban. All grounds are clearly marked and very important.
If the PO did not follow these color codes when he ran his wiring, then you have to interpret what he did. There should be a flat, white wiring connector that plugs into the igniter board with the proper color coding as shown in the diagrams. It's for you to decide if these colors follow thru to the switch and indicator light area.
If the PO is using a breaker as an on/off switch for the electric element, this will eventually wear out the break as residential breakers are not designed to operate as an on/off switch like marine breakers are.
You have to identify all of the wires you have, where they go, what the color code is AT THE WATER HEATER"S IGNITER BOARD and follow the wiring diagrams found in the manual.