The 194 side markers need to be an incandescent bulb. LED"s are polarity sensitive.
Not entirely true. While LEDs are polarity sensitive by nature, some automotive (and other) LED replacements are built/wired internally to not care about polarity. You can absolutely run LED 194 replacements in the corner markers of these trucks, but they need to be a non-polarity sensitive variety. Unfortunately they're not usually labeled either way. I know for a fact that these work, I'm running them in the corners of both of my trucks.
https://www.superbrightleds.com/mor...-bulb-1-led-miniature-wedge-retrofit-car/197/