fftfk. Do not crimp the tiny factory wires. Simply solder a length of heavier wire, like 14 gauge, to each aux/pass through wire.
Here’s one way:
- take an aux wire and a 14 gauge extension wire and put them together like straws.
- strip an inch or so from each wire
- twist the ends of the wires together
- solder the twisted ends together.
- let cool.
- bend the 14 gauge wire in a “U” so it extends the tiny aux wire
- put waterproof shrink wrap over the finished solder joint.
- the twisting, soldering, bending and shrink wrap add strain relief and strength to the splice. Should outlast the vehicle.
- now you can add your connector of choice to the heavier extension wire
This is way easier to do than to explain. Ask questions if not clear.
I recommend that you get Tony Candella’s books on automotive wiring.