The 1/4-inch output jack on an electric guitar isn't all that hard to replace. The jack is one of those things I change out before it breaks, if nothing else, the peace-of-mind is well worth it. Most inexpensive import guitars have a low quality jack that would benefit from this treatment.
The guitar under modification is a Squier Mini, an excellent guitar to learn mods, tweaks and setup with.
These are the tools you need:
Solder and Solder Sucker
Philips screwdriver, wrench, sockets and side cutters
Obviously, you need a replacement jack. The output jack on the Squier Mini is the cheapest import imaginable. For replacements I only use Switchcraft part number 12A. In fact, the exact same component is sold under several brand names. You should be able to get it for $2.00 or less. I buy them in bulk from Mouser Electronics and use the exact same jack for guitars and amps.
In the picture above you can see an inferior import jack compared with a quality Switchcraft. Visually, the main differences are in the shape of the contact blade. Less obvious maybe, is the quality of the nut, which is vastly superior to the import version. The Switchcraft jack is a more rugged design, so it will last longer and take more abuse.
If your guitar has a Switchcraft jack, there is no need to change it assuming it is working OK. There are import jacks that look more similar than the examples given here. However, the Switchcraft jacks can be identified by the trade name stamped on the inside flange of the grounding sleeve. It should have the name "Switchcraft" stamped on it. See picture below.
First, remove the jack plate using the Philips-head screw driver. Be careful not to scratch the finish of the guitar.
Removing the jack cup on a telecaster or jack plate on a Les Paul is about the same. Just make sure you use the proper size Philips screw driver for the screws.
Next, use the 12mm socket and remove the face nut. hold onto the jack with your other hand.
This jack was re-soldered not too long ago and the loose not tightened, so it looks tidier than most. Often the jack is loose which has lead to the wire getting tugged on, which often eventually leads to failure.
There may be other wires attached to the jack. Most common is a separate ground wire going to the bridge. Make sure all wires are connected the same as when you started. A good way is to take a couple of photos before you start disconnecting anything. That way you have a better chance to put things back together if this is your first time.
Cut off the wires close to the old jack and strip the insulation. In the picture above about 7/8" of the outer insulation and 1/4" or less of the inner has been stripped. Next, twist the strands together on the shielding and the lead. Tin the tips lightly using the solder iron and the solder.
Next, install the new jack. Use the 1/2" socket to tighten the nut. Note the orientation of the contact blade in the picture above. I placed a piece of board on the top of guitar to protect it from spatter from the solder. A better option would have been a towel or old T-shirt. I also placed a pair of pliers on top to hold it while I soldered.
Solder the lead and shield as shown above. Don't make it too tight.
Reattach the jack plate to the front of the guitar. You're done!