If i recall correctly on my 1990 vintage 3.0 was engine temp and oil pressure look and see on thermostat housing and stbd side of block you would need to see both a gauge sender and switch at each location fir them to alarm.I'm working on the wiring for my boat.
1989 mercruiser alpha one gen 1, 305 thunderbolt iv motor.
What trips the buzzer?
Just water temp and oil pressure?
Most of the boats have light or audio alarms. I prefer BOTH. Some also have low OD reservoir fluid switches. If working correctly, they go to ground when tripped. My buzzer was under helm. Unfortunately. most Chevy v8 oil pressure switches are located near oil filter. Difficult to replace.... I relocated and "T" mine into a SS 1/4" pipe next to my oil sender. U may also have a high-water alarm connected to a second bilge pump.I thought so. Thanks!