One wire will have constant power. Use a test light, ground the test light at the pillar, test the power wire, if the test light illuminates, you have 12V at the pillar.
Constant ground, make your own new constant ground at the pillar.
Switched ground......activated at the head light switch or the door switches. Use ohm meter, switch ground wire should show continuity with door open or with head light switch in the dome light position. If not, you have a ground problem. Touch one lead to the wire and one lead to the new ground you are making at the pillar, needle of ohm meter will move from one extreme to the other, if not, no continuity at ground wire......no ground.
Either way, if you have 12V at the pillar you can have manual light after making new ground at the pillar........then work on your door switches which you'll likely have to replace.