Ahem.... Its the wire your using... I learned something new in my investigation to buy a harness for my car. Also unfortunately the type of shrink you use and oh a little butyl for wire connections goes far.

For wires I suggest nickle plated TPFE coated wire. Stuffs expensive as hell but honestly worth it.
The copper ones especially aftermarket all creep like that a big pain in the *****.

For shrinking I highly reccomend butyl and high grade shrinks with lots of glue. IT should go Solder-butyl-shrink-butly-shrink-tape... Skip the tape..
That is how I do my car after doing 4gLTE instilations on cell towers which experience wicked wicked rain and wind and after farting around on marine connections... Actually on marine stuff I tell you what if I didn't pack it like that I just left the connections open and left extra wire to chop back and splice in. Want to talk about corrosion. The ocean is mean.

But enough rambeling. I clicked on the thread because it said the VTR never let you down and I feel the same way for mine. I hope my advice keeps your wires from failing.

EDIT: Yes the it will look like a big lump but itll be sealed. I also forgot to mention the first 3 steps are for 1 wire then the last three are for a group. If that leaks.... Ill just quit working on cars.