Q: no driver side brake light on 1990 Ford F-250

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
not getting power to brake light, driver side only,all other lights o.k. did replace socket and bulb before finding out I had no power.
(2) Answers
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There are several wiring diagrams to follow depending whether you have trailer tow package, cab package ect. Look at the side that has brake light working see what color wire is live when brake pedal is pressed and then see if that wire is live on the other side if not follow that wire back in the harness looking for a break or oxidized connection.
There is a company that independent auto repair shops buy their information from that the same information inexpensively to do it yourselfers. The information is year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate
Check the fuses, if you have done so already. Here is an online source for the wiring diagrams, you will need to trace down the brake light circuits to find the reason for the lack of power.