1st, are you sure your boat has the temp and oil switches installed? The audible warning kit was a pretty expensive kit for these engines. It would be added at the boat factory or at the dealer. It wasn't standard. The oil pressure switch didn't screw into the block, it was remote mounted on it's own bracket. Later years would have the switches stock but not the wire to the helm or a horn.
You will be looking for the tan wire with a black tracer on the engine. It will be at pin 24 on the EEC (ECU) then through a diode to the oil switch, then to the temp switch and then to the 10 pin connector at pin 4. There will also be a capped wire that was for future exhaust water temp monitoring.
Note that the temp gauge sending unit will have a solid tan wire and the oil pressure gauge will have a solid blue wire.
In the harness going to the helm from the 10 pin connector this wire might change to tan with a blue tracer or it might remain tan/black depending on the boat brand. If the boat didn't come from the factory with audible warning we would have to run a tan/black wire up to the dash because it wasn't in the harness.
The horn under the dash should have 3 wires, purple 12v from key switch, black to ground and tan/black that goes into main harness (or run separately) all by itself.
At the time this was built, OMC was worried about back feeding 12v to the EEC so they put a diode near the EEC and added a ground to the horn. Some boat builders didn't use a grounded horn, so I'm not sure if it's needed.
This system didn't have a beep at key on, it could be tested by turning the key on and waiting 20-40 seconds and the horn would sound continually. There is a timer built into the horn so it wouldn't sound during engine starting.
The way this system works is. when the tan/blue wire is grounded by the temp or oil switch, the EEC pin 24 is pulled to ground and puts the engine into S.L.O.W. mode and the horn at the dash is grounded by the tan/black wire so it can sound.
If I remember right the temp switch was screwed to the lower intake manifold to the starboard of the distributor. the oil switch was port side of the engine down low and towards the front.
You will be looking for the tan wire with a black tracer on the engine. It will be at pin 24 on the EEC (ECU) then through a diode to the oil switch, then to the temp switch and then to the 10 pin connector at pin 4. There will also be a capped wire that was for future exhaust water temp monitoring.
Note that the temp gauge sending unit will have a solid tan wire and the oil pressure gauge will have a solid blue wire.
In the harness going to the helm from the 10 pin connector this wire might change to tan with a blue tracer or it might remain tan/black depending on the boat brand. If the boat didn't come from the factory with audible warning we would have to run a tan/black wire up to the dash because it wasn't in the harness.
The horn under the dash should have 3 wires, purple 12v from key switch, black to ground and tan/black that goes into main harness (or run separately) all by itself.
At the time this was built, OMC was worried about back feeding 12v to the EEC so they put a diode near the EEC and added a ground to the horn. Some boat builders didn't use a grounded horn, so I'm not sure if it's needed.
This system didn't have a beep at key on, it could be tested by turning the key on and waiting 20-40 seconds and the horn would sound continually. There is a timer built into the horn so it wouldn't sound during engine starting.
The way this system works is. when the tan/blue wire is grounded by the temp or oil switch, the EEC pin 24 is pulled to ground and puts the engine into S.L.O.W. mode and the horn at the dash is grounded by the tan/black wire so it can sound.
If I remember right the temp switch was screwed to the lower intake manifold to the starboard of the distributor. the oil switch was port side of the engine down low and towards the front.