[THEFERMANATOR]

These pictures should be of the same set-up as yours as I have a 90 powerhead and early style harness. If you disconnect these 3 sensors and it still goes off you probably have a harness problem. There is also a chance that the self test portion of your hot horn has failed and stuck on. You can get a test light and connect the ground clamp to a 12V+ source and probe the brown hot horn wire and see if the light lights up. If it does then you probably have a harness problem. Also try unhooking the brown wire from your horn while leaving the key on and black ground connected. If the horn sounds it's defective, if not then your getting a ground in the harness. It doesn't take much to set the self test style horns off.

Here is the starboard overheat sensor.


Here is the port overheat, the one that hooks to the brown wire is the overheat and the white and black goes to the power pack.


And here is the fuel restriction sensor, you can also see the VRO amphenol in this one just to the right of the starter.