I have more of an electrical question.
My hot water heater will not heat when I try to use shore power.
I checked at the element with the switch on and I have 120 volts on both sides of the element with ground to the tank.
I replaced the element, the something.No heat.
I took a cord with a plug in and hooked it to the element, plugged it into the wall and the element heats up.
When testing I have 120 on the black but not on the other side.
When I am hooked up through the switch I have 120 on both sides of the element.
Is this an AMP issue? And if so how do I go about tracing that down?

Is this an OEM electric system or an aftermarket like Hot rod or Lightning Rod.

If it 's OEM, what is the make and model of the water heater.

Billy