It will be easier to do the soldering if you make up most of the wiring harness first before fitting it in the bass. Use some cardboard to make a rough template of the control cavity. Poke holes through the cardboard using the holes in the guitar body in order to get the spacing correct, put the pots, switch and jack socket through the holes (I normally do the nuts up as well so they don't move too much). You then get much better access to the pots for wiring, and it's easier to keep the wire lengths as short as possible so they don't make a mess once in the cavity.

You only then need to connect to connect the pickups to the selector switch (which can normally be done with the wiring harness still not fitted) and then fit the pots, switch and jack to the guitar body.

Don't forget to fit a ground wire from the bridge to the back of a pot. There should be a hole for this drilled from one of the bridge post holes to the control cavity (from the lower rear post hole would be my guess). When you fit the post support inserts, you'll need to run the wire down this hole, leave 10-15mm of the end of the wire bare in the hole and trap the wire between the insert and the side of the hole. I'd leave a reasonable length of this wire spare in the cavity to allow easy wiring up and any future removal.