Have RV Questions? Ask an RV Mechanic Online.
I just got in, can you get me the model of the tankless?
Also do you have a volt meter?
I think What I would do is just run new power and ground from the fuse box to the water heater and see if you can get it to turn on, so don't route the wires until you know it works. I might also invest in a cheap meter so you can test the voltage. I honestly have never been a fan of these tank-less water heaters, they are a pain to work on compared to the others. IF you wire it per the directions and use a new 12 volt source it should work. You could even go right to the battery for testing. Robert