Explanation: A blown black negative fuse, or any high resistance in the negative (ground return) path, can cause apparent low voltage. Marine electrical systems often use black for negative. When this path has high resistance (due to a blown fuse, corrosion, or a loose connection), a significant portion of the supply voltage is dropped across this resistance instead of being delivered to the transmitter. The transmitter effectively sees a lower voltage at its input terminals, even if the battery voltage is normal. A blown red (positive) fuse would result in no voltage at all. "Too much grounding" is not an electrical fault that causes low voltage. Antenna mismatch causes reflected RF power, potentially leading to the transmitter reducing its output power (foldback), but it doesn't directly cause a drop in the DC supply voltage reaching the transmitter.