Can't find Model number.

It is a 1979 Yamaha XS400F. Although it was built in 78 it is a 79 model year with that serial number. 392cc plus the serial number both ties up with it being an XS400.

Your original battery was a YUASA YB14L-A2 . Use that battery or an aftermarket equivalent.

http://www.yamahaownershandbook.com.au/?r=0

Try this link from the Yammy Owner's Club, members have downloaded a whole pile of manuals for free download, just enter your bike model.
Cheers.

G'Day mate
Check out this site to find the exact model of your bike from the VIN here. You can get a wiring diagram for your model from the Biker.net website. There is usually a mess in the headlight tub, lots of dodgy previous owner "fixes". Sometimes it pays to strip it all out and work your way through it. Happy to give you advice on the electrics of this bike. I have plenty of experience:)
regards robotek

It looks like Babbitts has them in stock. Go to www.babbittsonline.com/parts/viewbybrand/parts.aspx Please rate my answer.

No but your local Yamaha Dealer should be able to from the vin Number. It is generally on the Bike Label, or punched into the frame in several places, in some countries it is also on the registration disc.