boats of that era were equipped with the "standard" VP instrument panel, which did not include an oil pressure gauge. The engine was fitted with an oil pressure switch which breaks electrical
contact when the pressure is adequate and closes contact if the oil pressure is too low, sounding the alarm. This switch was mounted on the front of the engine, just above the crankshaft pulley and in most cases it has a single
blue and white wire running to it. You can test the system as follows: start the engine and remove the wire from the switch (careful of the rotating belt)...then ground the wire to the engine block. The alarm should sound and the idiot light should come on whenever the wire is grounded.
Later engines were equipped with an isolated electrical system
, and the switch had two wires connected to it, one black(ground) and the other blue/white. The test procedure is basically the same, except you ground the blue/white wire to the black ground wire.
You can easily test your sender or switch more or less the same way...Disconnect the wire from the switch and put one lead of an ohm meter on the switch terminal and the other lead on ground. When the engine is not running there should be 0 or very low resistance thru the switch, and when the engine is running the switch should be "open " or no continuity.
When the engine was delivered with the "deluxe" panel, which included an oil pressure gauge, there was an oil pressure sender mounted on the engine to drive the gauge. Usually this sender was mounted on a seperate remote
bracket and connected to the engine with a hose. This sender would have had a brown/white wire and a black ground wire connected to it.
My guess is that your engine is a late model version (production of the 2003 ended in'93) with the two wire oil pressure switch, and that is why it looks something like #4 in the schematic, but you can test it as described above.
Hope this is helpful.