The problem with split bolts is also present in the link last sent. Sharp corners that cut the tape with vibration. A properly crimped butt splice would be my thought.
It's hard to tell from your photo, but if one wire is Aluminum and one is copper, a contact paste for these dissimilar metals could have helped prevent this. Split-bolt wire nuts are also notorious for trouble, and last week I found one that had caused a fire that should have never been (another...
I just posted and forgot to state that it is for use with a wireless beltpack transmitter. Currently made for Shure or Audio-Technica transmitters, more brands by request.
there is a cable made for this, with a resistive network to safely combine the L + R channels (instead of shorting them together). It is called the Kenny Kable, or iKenny kable. http://www.rothsound.com/ikenny-kable-3-5mm-to-ta4f-shure-bodypack-transmitters-p-508