You will need to pull a black hot and a white neutral from the junction box to the switch box, then run another black and white (romex wire is fine) to your light box. Hook the light up first by just color coding the wires and cap off. Install light. The switch box now, the whites and possible ground wires just color code again and cap off the remaining two blacks go to your switch itself with power at the bottom for future reference and the switch leg to the light at top. Please be careful when messing around in the junction box and never ever trust anyone elses wiring
