Hi ashley can you post the year car was made, I'm not a sparky but you will probably get a better response to you're query from those that know if you could give a little more info.
Have had a look at a wiring diagram for a post 76 car it would seem the heater switch and wipers share the same feed 5/6 in the fuse box, Light green with white tracer from the ign switch and light green and orange to the wiper and heater switchs check connections are making good contact (Wires to fuse box and fuse to fuse box contacts) If you have a multi-meter check for continuity across the in out terminals of the fuse box with the fuse in place, failing that with the ignition switch set to on check you have 12v at the input side Light green white tracer.
Like I said i'm not a sparky so don't take my post as gospel, I'm Sure someone will be along soon who can give you a better explanation than I.
Edited by Stu1961, 15 January 2017 - 05:40 PM.