You want either heat shrink butt connectors that you crimp and hit with heat gun to shrink the wrap. If you have a good set of crimpers this is all you need. I used to do aircraft wiring and this is the way we did it. But we used high dollar crimpers.

https://www.amazon.com/s/ref=nb_sb_ss_i_3_16

Or get some non-insulated butt splices that you can crimp and then solder and then wrap with shrink wrap.

https://www.amazon.com/Non-Insulated-Butt-Connectors-22-18-gauge/dp/B000W20ZVA

Shop around. You can find all gauge sizes.

Some sort of crimp on may give the cleanest appearance. I like soldered connections. A minimalist approach uses a quality wire stripper to push aside insulation, exposing the conductor for soldering, without cutting the wire. Can fold all the wires back at the joint, if there is enough slack, and slide on a piece of heatshrink, or wrap it up with rubberized tape, or whatever. Not usually too concerned about appearances.

You want a red squeeze tap connector for 18-22 gauge wire. There is also made one for 22-26 gauge wire as used in telephone hard wiring.

https://www.homedepot.com/p/Gardner-Bender-22-10-AWG-Tap-Splice-Assortment-5-Case-15-2210/202522123?MERCH=REC-_-PIPHorizontal1_rr-_-202522457-_-202522123-_-N

They slip over the wire you want to tap into. Then you shove the new wire into the extra hole and squeeze with pliers.

These are called tap-ins at Radio Shack (they've got the small ones for 22-26 gauge wire in the telephone applications section), and squeeze taps by electricians.

Noooo Ken those are horrible and they are ugly. They do work though.

Squeeze taps look like ass...just solder and shrink looks 10x better

Yes, you can add the third wire for your "y" connection. It will not compromise the crimp.

When I was doing aircraft wire harness work, we were allowed to add one "filler" wire into the crimp to "take up slack". For example, assume you were going to splice two different gauge wires into a butt splice and on one side the wire was 16 gauge and on the other side the wire was 22 gauge. With a crimp size that allowed for 16 gauge wire, the 22 gauge wire would be too small to be crimped tightly. So, the solution was to add an extra piece of 22 gauge wire to take up slack and crimp both the 22 gauge wire along with the short piece into the butt splice. And then after you made the crimp you would cut off the extra wire from the short piece down to the butt splice. And then you would apply your shrink tubing and be left with a good tight crimp with 16 gauge wire on one end and two 22 gauge wires on the other.

This practice was written into our wiring specifications and approve by the FAA. We crimped and added shrink tube. We did not solder our crimps with our aircraft wiring. It was not required. But we used the insulated water proof shrink tubes like these:

https://www.amazon.com/HOODDEAL-Insulated-Waterproof-Electrical-Connector/dp/B015LXQTK0/ref=sr_1_8

or these:

https://www.amazon.com/Eventronic-Electrical-Waterproof-Automotive-Connectors/dp/B0722W1718/ref=sr_1_7

In your situation, you could also place a small piece of filler wire on the other side if needed. Say you are butt splicing 16 gauge wire on both sides all you have to do is add your wire to make the "Y" then you would also add a short piece of 16 gauge filer wire to the other side, then cut off the excess and follow with your shrink tube. This will give you that good tight crimp on both sides and you would not need to solder; However, because I am using cheap generic shrink tube like the stuff you buy from Autozone or Harbor Freight, I like soldered connections and I would solder and then follow with with the shrink tube.

I would like to clarify that I don't solder crimp connections when I am re-pinning the connectors that fit in the circuit board because it is not needed. And a good butt splice doesn't need soldered, either, but soldering will give you a more solid connection.

Sorry to get carried away and get so wordy. It is a fault of mine.

Personally, I don't like using crimp or press on connections on anything that is going to vibrate or move around, unless it is a crimp and solder combo.

If I were wanting a secure splice on a wire like that, assuming the wire has to be cut, I would :

Strip long

Twist up one end of original wire with new added wire

Slide on piece of shrink tube onto doubled wire

Slide another shorter piece of shrink tube (may need to be a size smaller diameter shrink) onto single wire

Take twisted wires and combine with other original wire via a lineman splice kind of style for mechanical connection

Solder all three together

Slide single wire shrink up to soldered splice (only over single wire) and shrink.

Slide double wire shrink over entire soldered splice and single wire shrink tube until flush at other end and shrink. (This way the single wire has that piece of shrink over it to make it fatter so outer piece of shrink that covers whole thing is more evenly shrunk down ... may be mostly cosmetic, but I feel it can help keep the soldered splice from tearing through the shrink sometimes).

This creates a nice solid mechanically sound splice; it may be overkill, but I like doing things once.

Notes:

Depending on situations like if I am worried about shrink slipping around or moisture, I may use adhesive shrink. Or, I may use a second outer piece of shrink (so 3 total piece) if my shrink tube I am using seems cheap/thin (admittedly, this adds thickness and doesnt look quite cad nice).

Notice I did not solder any wires first. All twisting of wires should be done first. If you solder first then twist, you are trying to twist a solid hard bundle that may lead to cracking and a potential damaged wire (now or noticed later)...stranded wire is stranded for a reason (well several reasons-depending on application as well).

Side question - why do I see a red wire having a black wire spliced into it??? That's just asking for trouble to me...

Like I said, this is just one method for a solid connection. I am sure there are many more, and most any mentioned already would probably do the job for this application.

Edit : people, PLEASE use a heat gun or other hot air to shrink the tubing...why do I see so many people thinking lighters or flames of some type are how you use shrink tube???....

You mentioned it not being required to solder after crimp for FAA. I believe it. I recall some military specs on equioment I've worked on in past where the specifically state soldering after crimping (a pin or connector) is not allowed. Their theory is that the rigidity of the hard soldered end is more likely to crack and break under heavy stress/vibration that the stranded wires when properly crimped (with the recommended zillion dollar crimpers of course. Lol).

On my home stuff, I typically don't solder crimped pins etc, but do like to solder on things like crimped ring/fork terminals when I can...I like knowing it isnt going to come off. Even though a good solid proper crimp really shouldnt anyway as we know.

Extra note - it was also required to be lead solder when we did solder work.

Does FAA require lead solder still? Just curious, don't want to side track thread too far

I'm sorry. I partially misspoke. On some of the jobs, while we did not solder directly with a roll of solder, the shrink tube we used was insulated shrink tube with a ring of solder on the inside. Once the crimp was made, we used a heat gun with a special "U" shaped end that would apply heat evenly around the shrink tube and melt the solder to the wiring.

These shrink tubes have that ring of solder inside. It is a metered amount and fully encased within the tubing. With heat, the tube shrinks, the adhesive on both ends melts for waterproof protection and the solder melts, fully contained with no solder drips anywhere.

And we used the AMP crimpers that cost about $300.00 each.

https://www.amazon.com/Eventronic-Electrical-Waterproof-Automotive-Connectors/dp/B0722W1718/ref=sr_1_7

The wiring that did not get soldered was when a connector pin was crimped on and installed in a cannon plug. With a cannon plug install the connector was shoved/inserted inside a chuck of silicone rubber for 100% moisture proofing.

Xlr-connectors (resized).jpg

Man, I love cannon plugs. If they were not so expensive, I would rather use them instead of Molex connectors.

Same here. I like to use unprotected ring terminals so I can solder them but they are hard to find. My local hardware store has, unfortunately, quit carrying them.

imgres-2 (resized).jpg

Lol, I've soldered insulated ones and when plastic melted/split off wound up adding a piece of shrink (adhesive if I have it large enough on hand) over it.

I don't think I've ever used anything with solder already inside it. Very interesting!

These are the types of threads that remind me how Pinside can be great!

Lol. If it wasn't for the excuse it provides me to solder on a regular basis I probably would have given up pinball years ago!

Few things are as instantly gratifying as desoldering, soldering components on a board and having it look 100% when finished.