z50king

i just set up a outdoor gazebo for my aunt and she wants me to wire in an outdoor light for it. the gazebo is setup next to where her spa used to be but the spa is gone now. their is still the control box housing all the wiring from the old spa. it has the timer and all the relays and stuff in it. i followed the conduit back to the house where it has its own box with two 40 amp breakers in it. the switches are tied together with a bar. this box is seperate from the rest of the home circuits. since the spa control box is still there she wants me to tie this little light into one of the hot lines. i have no idea if this is safe or not. i know how to do electrical work, but i dont know if its safe or not to tie into one of the hot lines going into the box or not. i have access to all four lines before they go into the box. has two hots, one neutral, and one ground. they are laaaarge guage lines thanks, and im a newb to this site