Running lamps on, blinkers & brakes dont work

[threetoedshewie]

Model: 1978 Malibu
Case 1: head lights and tail lights are on :arrow: rear turn signal and brake lamps don't work
Case 2: head lights and tail lights are off :arrow: rear turn signal and brake lamps work
I have checked and cleaned the ground to the tail in the trunk and cleaned the connector in the trunk. the bulbs are all good and I also have back up lamps.
everything works, just not together.
does anyone have any ideas or maybe a link on what all the symbols on a Chevrolet factory wiring diagram mean?
I have already searched the forum for similar problem and found the one titled "Relay?" where one member linked a similar problem to the "blinker harness assemble." could someone explain how he did that? and where the blinker harness assembly is?
thanks. :?:

 

[SBCregal]

theres a harness in the trunnk, on the left side (i believe its green, not sure though) all the lights at the back run through it. when my brake lights didnt work, there were 2 broken wires at that harness but when i picked it up and started making connections, the rest basically fell apart and everything else stopped working back there

had to completely rewire those connections, i tore the harness out and used male/female spade connectors. all the connections work now. it takes up a bit more space, but its all hidden under anyways