Have read all the posts on fuel guage issues, checked the wiring and still have a situation where when full the guage reads full. But after using approx 15 l, 4 gallons, it starts to flick between zero and full and at about 20 l used drops to zero where it stays. Could this be a sender unit?
Cap : It sounds as though your fuel sender needs to be replaced.
Till you replace the faulty sender and get it back up, just use .5 gal/hr for your fuel consumption.
Easy to do - just follow the info in posts, in projects and in Mainsheet tech notes.
Or, you could consider using your fuel gauge to be your engine hour meter, like this:
http://c34.org/bbs/index.php/topic,3841.0.html
Senders die, simply because of the way they're built and the way they work. Replace your sender (only once) and check the gauge just before you sell your boat. :D
Thanks for the advice. Now have spreadsheet on my iPad