1966 Mustang GT - Courtesy/Interior Light issue

[Veneratio]

Hi, everyone. I have posted a couple times before and you have been a tremendous help.
My latest problem is my Courtesy/Interior lights will not come on. This is what I have done:
I replaced all the bulbs, door switches, headlight switch etc. I checked continuity of the wiring, I double checked all the grounds - all seems good. I pulled the fuse box, everything is clean and seems good. But I cleaned and replaced all the fuses and the connectors anyway. I have not replaced the wiring harness - trying to avoid that. I mean as you all know a lot of work.
Now if I give 12V power to the Black/Blue wire #53 on the headlight switch plug - all the lights come on without regard to the position of the door switches.
I can not figure out why the courtesy/interior lights do not seem to get power without the external 12v power source.
Any suggestions/ideas etc would be very much appreciated. Super frustrated right now - been working on it for several weeks.
Thanks

 

[Veneratio]

Hey Guys, I located the issue. Some time ago, someone installed an in line fuse in the Grn/Yel line. I located the fuse, although it tested good, I replaced it and everything works like it should now. This had me stumped, but feeling good now. Just wanted to let everyone know how this issue was resolved. Thanks

 

[COramprat]

Electrical issues are hard to diagnose. So many factors that lead to issues. Cool you got it fixed.