Swap a string by putting your top string in place of the second.
If you take it off carefully and put it onto the second post, and wind it more times, it can still go back on properly, although a new set of strings isn't extortionate.
If this string is still quiet, it's the pick-up, although it's doubtful all three have the same problem.
More likely it's the string itself - which you can check by putting it in place of the third string.
An acoustic string just doesn't do it on an electric guitar, but it may look alright.
Or, simply get a new set of strings anyway.
music.stackexchange.com/users/2808/Tim
Unless it is an acoustic guitar string (nylon or wound with non-magnetic material) or clearly not vibrating, it's the pickup that's broken: any wiring possibly connected to the strings is just to reduce hum, not change the signal level.
The pickup reacts perfectly fine to an entirely unconnected string if it is an electric guitar string rather than an acoustic one.
I think that the coils are usually wired in series, so if you still get sound from the other strings, there are rather few error scenarios I can think of: a) coil is shortcircuited.
This will most likely be purely mechanical: two items touching that shouldn't.
b)
magnet is dead and/or has fallen out or there is some other break in the magnetic connection in the pickup c)
someone disassembled the pickup at some point of time, the pickup is a double-coil pickup, and one of the coils or one of the magnets was put back in reverse.
Double coil pickups are intended to pick up outer magnetic fields in a manner that the voltage inducted into both coils cancels while the voltage induced from field changes done by the vibrating string to the field from the coil magnets adds up.
Reverse a coil, and you pick up the noise and cancel the sound.
Reverse a magnet, and both noise and sound cancel.
music.stackexchange.com/users/13147/user13147
A guitar pickup in 99% of all guitars including strats is a single coil of wire which senses all strings at the same time.
Some pickups use individual magnets for each string, a fender Stratocaster for instance, and some use a single magnet underneath the pickup but have metal slugs or screws directing the field of sensitivity towards the strings, such as a Les Paul.
This is irrespective of whether or not the pickup is a single coil or a humbucker, but in most situations it ends up the way I described.
However some cheeper pickups such as those found on some squire strats do in fact use a single or double magnet underneath the single coil to create the magnetic field for the pickup to work.
What I am getting at is that in all likelihood the fact that the pickup senses the other sttings would indicate that the pickup is perfectly fine.
Without seeing the guitar i would guess the string is not resting in the slot properly.
Most likely at the bridge.
If the problem would be at the nut slot, then fretted notes would sound out well.
So make sure the string is seates well and if the problem persists you may need to smooth some type of burr on the bridge saddle that occur sometimes.
music.stackexchange.com/users/13158/smiley
This happened to me but only on the G string of my middle pickup.
I took the pickguard off and there was a ground screw with a wire not connected to anything in the cavity right below the pickup.
The screw was evidently touching the pickup magnet and making it so it wouldn't sound when plucked.
music.stackexchange.com/users/65281/Steve
This just happened to me:I thought it would be a good idea to clean the metal particles gathered on my pickup pole pieces with a strong “rare-earth” magnet.
After doing this, I completely lost any pickup volume for my A string only.
I quickly realized it was because the magnet reversed the polarity of that one pole piece.
The solution:Touch the other side (other polarity) of the rare-earth magnet back to the top of the pole piece.
If this happens to you, it’s ok if you get the wrong side at first.
I hope this helps someone out.
music.stackexchange.com/users/69298/pwurso
I played a Squier Stratocaster last night, well, when I plugged into amp, which it's working, my guitar's second string didn't make any sound - well, a bit actually - but the rest of the strings sound normal.  Is the problem is on the pickups' coil or the guitar wiring? When I tested the other pickup position (I used Hendrix-like middle+bridge) like bridge or even bridge, the second string still didn't make any sound.
Guitar: No sound from second string, but other strings sound normal
music.stackexchange.com
<guitar><instrument-maintenance>
music.stackexchange.com/questions/23091
music.stackexchange.com/users/9248/seseorang
If a string on an electric guitar is not playing, it may not be resting in the slot properly. To test it, put it in the place of another string. Unless it is an acoustic guitar string (nylon or wound with non-magnetic material) or clearly not vibrating, it's the pickup that's broken: any wiring possibly connected to the strings is just to reduce hum, not change the signal level.   The problem could be with the pickup, but it is unlikely. The problem is more likely related to the string itself.
The problem is most likely to be the string itself. Unless there is a problem with the string, the problem could be with the pickup, although it is unlikely.