Ok, doing a stereo install on a 92 Civic. The constant(B+) wire isnt gettin any power when the car is off, and when its on it reading at about 2 volts. The switched power works like it should. The B+ isnt gettin a complete 0 when the car is off, its jumping around in mv's. Any ideas whats wrong?

blown fuse maybe

Checked that and its fine, the radio is on the same fuse as the cigg lighter, and thats working.

If you are getting 12V constant at the fuse but not at the head unit, then I'd say there might be a bad connection in the radio wire harness, bad solder or crimp in the new harness maybe...

Voltage is fine at the fuse. I think im just gonna run a wire from the batt and use that as the B+. Id need a 15A fuse on that right?

yeah you definitely need to fuse it. I don't know why you wouldn't get any power to it though.