Sounds like you have a toilet that doesn't draw from the water tank, it uses sea water Trace the toilet inlet line to the thru-hull and open the seacock.
What's the make/model/age of the toilet? If you don't know, I can ID it if you'll post a photo. Once I know what you have I can post a link to the owners manual for it.
However,....depending on its age and how well it has or hasn't been maintained, it's likely to need some work that may or may not cost more than replacing the pump and motor. So after you've succeeded in getting water to it, the first thing I'd do is put a volt meter on it WHILE FLUSHING to determine whether it's getting a full 12v. If not, it's either a wiring issue or a weak battery. We can figure it all out once you get water to it, find out what you have and determine how well it's working.
Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
