I have a 78 124 and recently the headlights stopped working, just today i realized that the windshield wipers are also not working, as well as the heater. i suspect there is some fuse that has blown, but i con not seem to find it. Would anyone know where it might be located?

According to the workshop manual wiring diagram, the wipers and heater are on one fuse and the headlight beams all have seperate fuses in the under dash fusebox so unlikely that 3/5 fuses would blow at the same time.

As they are all ignition controlled consumers, more likely to be the power supply wiring or connections between the ignition switch and fusebox.

You may want to check the ignition switch connector - all power goes through it. Also, to reduce the load on the ignition switch, headlight switch and column mounted high/low beam switch, you should install headlught relays.