1972 blazer electrical problems

[bsager79]

Im new to the site and tried searching to see if this issue had been covered but the search option wouldn't work.
I have blinker, hazard, brake light, and back-up light problems.
When switching the blinker in either directions all of the blinkers light up. When i apply the brake and hold it all blinkers light up. Hazards dond seem to do anything. The back-up light fuse was missing, but when i put a fuse in it the started flashing rapidly.
Im lost. Everyone tells me its a bad ground but i dont have a clue where start.
Thank you in advance to anyone who can help.