did a search and a old post joe reeves (well respected guy) said and I quote "The vaccum switch enables the warning horn to sound constant and steady if a fuel restriction is encountered"
They have a updated number for the switch but they are proud of that made in china plastic piece to the tune of $130 new or $30 used. I can not link the site I normally use to show parts diagrams but a quick yahoo search for gt150 Johnson vacuum switch should lead you to a site that starts with marineengines just enter the engine serial number to get to the parts diagram or enter the year and type. hope this helps
