So I noticed I don't have a reverse light, first things first I checked all the fuse, bulb and even the reverse light switch and all of them are good still I have no reverse light. And I did some “troubleshooting” and checking all the continuity of the wirings, the wiring connector that goes at the back is good. Next I checked the Green wire with a Black stripe on the engine harness(the one that is connected with the switch) going through the harness that goes at the back and there is no continuity. So my assumption is there is a wire that’s been cut between the connector in the switch through the harness connector that goes at the back

here are some pictures of the wire harness connectors:

the one on the engine connected with the reverse light switch

female harness connector going through at the back harness

male harness connector from the firewall

 

Was your chassis originally an automatic or manual transmission version ?

 

its originally a manual as far as I know.
it has a reverse light before

 

Follow the wires back from the lights forward... wherever you lose continuity, you may have to run new wires from that point up to the grey connectors that you have illustrated above.