sending unit
 

can anybody tell me how the wiring is ran between the sending unit ,ignition switch and fuel gauge

Hot wire from the ignition to the gauge itself, usually the "I" terminal. Ground from the ignition to the "G" terminal. Also a wire from the "G" terminal to the sending unit. Then from the "S" terminal to the other post of the sending unit.
Connect the light wire to the instrument lights.

OH, and there are other ways to bastardize it too!
Dis don't help, holler.

Its never going to work right and if it does it won't for long!!

I fill after each trip and have never had a issue!!

Now I have a bigger boat that holds 110 gal and do the same, have been all over and never think about gas, O yea and it has no gas gauge either!!

Yes, but the HOLE for the sending unit does make a convenient access hatch for pumping out water in your tank:clap:

sending unit
 

OK then,can anyone tell me how many gallons this tank is.I heard they have an 80 gallon but dont know!

See if this is correct for the '78, 58 gallons with the original tank.
http://www.wellcraftv20.com/gallery/cat_1978/10_G

And update your signature/profile too so I ain't got to look so hard.:bat:

they have twin saddle bags =40 gal

They have a 60 gal in floor on the 80's and up.

the older in floor tanks were like 40 not 100 %??

But there were none more then 60 unless some one added to it.