I saw a few threads on here where people asked how to change this behavior, but none contained an answer. You can stop the game from automatically shutting off your turn signal when the steering wheel returns to center by commenting out the logic within manage_automatic_indicator_stop() in lua\vehicle\electrics.lua: My simrig has a physical turn signal stalk that doesn't have a servo/stepper. This change to electrics.lua allows me to keep the game and signal stalk "in sync".
I know absolutely nothing about programming so I'm not trying to edit the wrong thing and mess it all up so please show me like a picture of what it edited should look like.
Just set the local controlPoint value to 1000 or some other unrealistically high number. Deleting something caused my game to break.