Help with new gauge setup

Gauges installed over the past couple days! Everything but the oil pressure line is hooked up and working. Please excuse the ugly zip-tie mounting as I don't have a drill handy. I may actually leave the ties and just cut off the ends.

Looks like voltage is kind of high at 15.5V - from reading around, it sounds like that's usually caused by poor connections somewhere between the alternator and battery?

Oh, and I ended up going with the spot in pic #2 for the temp sender as it was easier to get at and closer to the firewall hole I wanted to use. That puppy was pretty stuck, finally got it by sitting on the passenger side quarter panel and using my foot to turn the wrench.

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