Later, the numbers were printed on a vinyl tag. First, these would be on a metal tag and stamped with the numbers. On later model Mercury engines, the serial number was located on the swivel bracket, as shown in the picture below. So long as you know your HP and the serial number, you can identify the year of your outboard. That freeze plug will have a serial number on it. If for any reason that number may have been changed, removed, or can no longer be read, every Mercury had a freeze plug, which is on the powerhead and about the size of a quarter. On older Mercury outboards, going back into the 50's and possibly even earlier, the serial number would generally be viewed at the leading edge of the swivel bracket, as seen in the image below. I'll try to be as complete as possible below, while keeping this reasonably simple. Over the years, manufacturers have changed where this information is located on an outboard.
