That s/n comes up as a model:
1075412ZD MERCURY 2002 75
Parts listing:
http://www.crowleymarine.com/mercury-outboard/3374.cfm
SErvice Manual P/N: 90-830234R04
http://1manual.com/Mercury manuals/Service Manual PDFs/TwoStroke/830234r3/cover.pdf
You must have Adobe Acrobat reader installed to use this manual. If you scroll down to the lower part of the opening page, you will see the various engine components in red. Click on the one you want and when the first page opens, click on the "Save As" icon at the top LH corner of the page and you can save it to your computer.
Look under Fuel System (Oil Injection) and it will show the wiring, tests and warning horn system for the low oil level. You will also see the Low Oil/Overheat Warning module which provides the two signals through tan and purple wires to the warning horn.
Gerry