5V conversion help needed

All I can offer... Ring terminals beneath speedy nuts for connections are too iffy. The speedy nuts tended to loosen over time even when they had full circumference footing.
So a better way... Place the speedy nuts just like OEM ( no shrink or isolation required ). Place the ring terminal on top of the speedy nut. Internal tooth washer and standard hex nut on top or the ring terminal. The attempt to isolate your red wire from that gauge post seems odd to me. You say the limiter is somehow disabled ( I wont get into the "bend the little thingy" BS here ).
Although it doesn't really matter where you tie into the 12 volts, the fact is red wire/12 volts no longer needs to go to that gauge at all.
Blue with white tracer in that round multi pin connector is switched 12 volts. Just tap your red wire into that. Where that blue with white serves no other purpose/component you could clip it from the round connector and make it to your red with male/female spades ( insulated female on the blue w/white of course ). Plus the different connector types means more difficult to hook up wrong in the future. Your orange wire could be placed on the wrong post in the future. Its in the right place today just not in a very good manner. Hope this helps