One thing after another, now I think I have a short somewhere......

[CamperSpecial01]

Hello. I have a 77 c20 camper special. . My dash lights went out, and I saw that a fuse was blown. I replaced the fuse and it fixed it. That is until I shifted into reverse then it went out. I put in another fuse, and it worked again, only until I shifted in reverse, but now, both tail lights dont work, and the driver side rear blinker, and brake light don't work. I traced all the wires to see if they were bare and touching metal. I also checked the bulbs, and even cleaned the ground wire in the tail lights. I am completely lost on this, and I want to avoid bringing it to a mechanic and paying tons. Does anyone have any suggestions what this could be, or what I should do? Any advice would be much appreciated.

Thanks a lot of your responses, sorry for the length. God bless.

Matt