Nothing wrong with trying to do what you haveout of interest, had i aimd to be less Macguyver, and more like someone who does this properly, how should i have tackled the problem? what parts am I missing, could have ordered etc? Learning.....
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If you wanted to be able to easily disconnect, you could have gone the DC jack route.

The positive and negative terminals are clearly marked. And it would have negated the need to cut the barrel jack off ( If it fits. They come in different sizes )