I retain "idiot lights" as they are the only thing the driver can notice while busy. To that end, I use big bright ones, common clearance lights are good as they are easy to see and can be written on so you can't miss knowing what just failed. More recently I have found that illuminated game switches are better looking and almost as easy to see. ( one just tosses the microswitch away).

I destroyed two engines that had no lights. there is not time to peer down at a gauge while running hard so I place lights at the top of the dash near the driver's line of sight.

As to "t " fittings, I use them as they are so convenient and I like having lights along with gauges.
thinks for the warning about them splitting, (guess what I'm going to check tomorrow)..