Most people who want to keep the original steering buy an aftermarket controller that is clamped to the existing steering column and has the turn signal arm and the brake/turn circuit within it. If you didn't want it to show, you could install it behind the dash with just end of the the arm hanging down and push it to the left for or left turn or right for a right turn. With just a toggle switch, it would be a lot more complex to get it to work, or you would need two separate light assemblies on each side with turn lights only on one assembly.
