I take it from the name that a Sun Jet is a Chinese import? My son owned a Chinese scooter and I can tell you that the electrics are a little "fragile". Assuming that the new battery is both charged and not defective, you could have caused a break in one of the cables + or - when you disconnected them. I had to run new earths from the battery and the engine on my son's scooter.
Also as Perry says, the fuse is a good place to start with diagnostics.
Cheers
westcountry, October 2013
