Replaced factory cluster w aftermarket. Turn signal issues

We just recently went through this with another owner. There are up to 3 components that require switched 12 volts. Gauge voltage limiter, oil warning lamp, and brake warning lamp.
If you dont have a blue with white tracer the only switched 12 volts to the inst' panel will be black. They changed this in different models. In some builds the blue with white tracer supplied the gauge voltage limiter only which is grounded to the panel. In other builds the blue with white tracer supplied 12 volts to all 3 components. In other builds a second switched 12 volts was black and supplied the oil warning lamp and brake warning lamp. In later builds the blue with white tracer was deleted. The single black wire supplied all three components.
Those lamps are grounded at those remote switches. That's why these lamps had 2 copper traces to wires instead of grounded to the panel like illumination and indicator bulbs. For example, oil warning lamp got 12 volts on the black or blue w/white and ground on gray. The brake warning lamp could get ground from 2 switches. One at hand brake switch inside and one at brake fluid system pressure switch on proportion valve. I think those wires were either black or tan. I'm really only guessing but I believe the black wire you refer to is to brake warning switches. Hope this helps.