B190 Enthusiasts

Following up on this old thread for heating holding tanks during the winter. I have ordered Facon holding tank heater. I am struggling a bit for wiring it from holding tank to the area close tower pump control and water heater switch. Does anyone know where the wires from holding tank sensors enter the vehicle? I need 1-2 locations in between the holding tank and the switch (near water pump) to fish the wire. Thanks.

For anyone wanting to install a tank heater pad, I ended up using the hole underneath the couch. There is a hole there for AC grounding, main coach battery input, etc.