Where the wire hole is depends on the style of bar pickup. There are 2 styles I've used, one is aimed at violins with the wire exiting from the center of the bar, the other is the more common bar with the wire exiting from the end. Both are a bit longer than most fretboard widths, about 1 1/2 -1 5/8 I think. There may be shorter ones available. The end exit type can be carefully clipped shorter. The active elements are seen as small bumps in the skin, the cut S/B between the last 2 bumps, there 4. A good set of side cutters works. The hole on the end exit style is drilled right next to the fretboard and the wire/bar end covered with a lightly glued cap.
There are some that already have the bridge piece glued to the pickup element. I've not used any. I make the bridge to fit.
The wire can be fished out the jack hole with a piece of cutoff melody string with a hook bend on the end.
Use a pencil type soldering iron with a non corrosive, electronics flux core. Apply heat to the jack tabs to melt the solder not the wire.