ST-1 body barely audible when testing pickups with magnetic screwdriver

[fender3x]

You should be able to hear a very clear, relatively loud sound when you touch a heavy metal object to the pickup. Make sure you're using something big enough. A small end-wrench (spanner?) is better than a screw driver. Something with some ferrous metal mass.

It sounds like it is either grounding out somewhere (as TD suggested) or you have a loose or cold-soldered connection (as TD also suggested). Starting with the jack is a good idea (...TD again...does it seem like a pattern is forming?).

One confusing thing (at least to me) about your wiring is that all the black leads seem to be grounded, and MOST of the yellows seem to be grounded as well. The exceptions seem to be the yellow lead from the bridge pickup, and yellow lead from the middle lug of the volume pot to the jack. Check the black wire solder joint at the jack. Also check it at the other end. From the pics I can't tell where the black wire ends. It should be grounded to the case of one of the pots.

If those connections are good, check the yellow wire's connections: To the middle lug of the V pot. the other end looks good, but checking won't hurt. Next the red wire's connection from the switch to the V pot's lug that is closest to the switch. If that's good, check all the casings of the pots and switch. All of them should have a good connection to the ring on the jack.

[Trevor Davies]

...
One confusing thing (at least to me) about your wiring is that all the black leads seem to be grounded, and MOST of the yellows seem to be grounded as well. The exceptions seem to be the yellow lead from the bridge pickup, and yellow lead from the middle lug of the volume pot to the jack. Check the black wire solder joint at the jack. Also check it at the other end. From the pics I can't tell where the black wire ends. It should be grounded to the case of one of the pots.
...

The ST kits are preloaded. So, the mixing of the coloured wires was done in the factory. It is quite frustrating. The factory could at least pick a common ground colour.

[fender3x]

The ST kits are preloaded. So, the mixing of the coloured wires was done in the factory. It is quite frustrating. The factory could at least pick a common ground colour.

It makes no sense to me that the two leads that run to the jack are both colors used as grounds.

I think the advice about re-soldering the leads at the jack is good. Also the black tape. If that does not work, I am guessing the problem is here somewhere at the V pot:



What it should look like is that the upper lug should have the red wire from the middle of the jack and nothing else.
The middle lug should have only the yellow wire going to the jack attached.
The bottom lug should be soldered to the case along with the black wire to the jack, the black wire to the bridge and a yellow ground wire from the 1st T pot.

The only other place that looks like it might be the culprit for a short is that star ground at the 1st T pot, since it grounds all the pickups.