Proud owner of a new Hat (new to me!) Have a few questions

[Hat43c1981]

I wanted to first say thanks to the moderators for accepting my request to be a member of the forum. I look forward to learning more about our boat from you all. 1981 Hatteras 43c w/ DD 6V92’sFew tech questions. * Need help with light switches and what all they turn off and on. She has almost as many residential light switches as my house! Is there a diagram in the owners manual?* The water heater does not turn on/pull any amperage. I am guessing the element is bad. Not much identification on the unit and it appears to be the original unit. I have attached a picture of the only identifiers I can locate on the unit. Would you replace the entire unit with a new unit? If so what would you suggest I install? Or would you suggest replacing the element? If so where would I purchase an element from for these older units? Thanks in advance for any help you all can provide! Take care and stay safe!