Sunnybrook hot water electrodes

I am trying to help a friend who owns a SunnyBrook fiver and he says the electric hot water doesn't work. I pulled both the red and brown wires in the outside panel from what I think are going to the electrodes to test with an ohm meter. He thinks the electrodes are behind the metal box under the sink. I am now thinking that the wires outside are too small in gauge to run a hot water heater. They look like 12v.
Do we need to remove the metal box under the sink? There is an on/off switch on the metal box as well as on the wall.