electrical question 87 ranger

I just installed a Sunpro super tach II onto my steering column got it operating fine i just find myself unable to locate a fuse or wire on or around the fuse panel that gets 12v + only when the headlights or parklights are on it doesn't have a taillight fuse apparently or I'd jump it from there does anyone else out there have a similar truck with a tach that can lead me to such a wire so i can have the illumination on my tach without having to pull the guage cluster out to feed from an instrument light. Any help or advice would be great, thanks in advance!