Before I crawl under the dash

If you can pretest every single gauge prior to locking the dash back in place that is a win (Captain Obvious here) Plus you just can’t have to much light under there. Have your flashlights set up and tools within arms reach. Long needle nose pliers are also your friends! And plenty of zip ties to keep it routed how you want it. Does not hurt to have a helper handy. They can fetch whatever you forgot or need so you don’t have to unfold and climb back out! Good grounding is key key key. I typically sketch out a schematic prior to going under then take it with me, as I think I will remember this or that and invariably I forget. Good luck, working under dash is miserable unless you are a elf!