The yellow on the negative is probably the radio ground. Radio should have at lease one fuse in the back of the unit.
Probably a fuse panel under the helm near the gauges.
Battery selector switch, or the wires connected to it, may be fried.
Check your ground to make sure it is clean and tight.
Consider getting a probe tool, it's not expensive and will really help with electrical troubleshooting. Got mine for 20 bucks on amazon- ultra probe 3.
2006 Bayliner BR205
A1 Gen 2 1.47
5.0 carb engine