Did you use regular electrical tape? I strongly suggest only ever using heatshrink on electrical splices (I started strictly using the bare ferrules (or soldering) and heatshrink a few years ago, rather than the ones with the red, blue, or yellow plastic over them). And if it's exposed get some liquid tape and coat the splice with it first then put the heatshrink over and shrink it down (then it's completely weather tight). An alternative to heatshrink if you can't manage it because of the splice is to get what's called splicing tape, Lowes has a couple versions from 3M, one is pretty pricey at $10 a roll, and is super thick. The other is a bit cheaper and thinner (I haven't tried that one yet, I have the more expensive stuff to use with my antenna connectors for Ham radio). Both will relatively instantly vulcanize and permanently bond to itself.
Another option is to get some of the fabric tape like the OEM's use for binding together wiring harnesses, I think it's called friction tape. You can get a roll at Lowes for a few bucks. They also have non-adhesive vinyl wrapping tape. Really, anything you need for proper splicing (or wiring harness binding) can be had at Lowes, they have a good enough selection of tapes for this stuff, and I believe you can get heatshrink there as well, but I get my heatshrink from a local dedicated electronics shop.
Regular electrical tape, even the really good 3M stuff, isn't super reliable, especially in temperature extremes. It doesn't like to stick to itself, since honestly it's not really designed to, as there is no liner for the adhesive when it's on the roll. I think the adhesive is more to kind of help with creating a moisture barrier, but even then it's not very good at it.
Honestly the only thing I use electrical tape for these days is at work to bind up the stacks of backup tapes before putting them into the carrier to be sent up to the vault in the mountain. I haven't bought any myself in probably a decade.
So to recap, crimp or solder and use heatshrink for the best splice, or if you can't use heatshrink use some self-vulcanizing rubber splicing tape. Or the fabric adhesive friction tape, though that is better suited for wiring harness binding (when you don't want the bulk of split loom). There is also non-adhesive vinyl wrapping tape, but again, that is best for binding wiring harnesses.