Warning horn not getting ground

[Jeanric]

I have a 1994 OMC Cobra Ford 5.0 Engine. The warning horn does not work, whether when I turn the ignition on, or when I simulate a failure by grounding the oil pressure switch.
It gets +12V through the purple wire, but not -12V through the tan wire. Where should I look next?

 

[jimmbo]

Try grounding the Wire that Goes to the Pressure Switch, with the Ignition on.
Of course the Horn, might for be an Overheat

 

[Scott Danforth]

make sure you are grounding the correct wire. If I recall, there are 2 connectors between the temp switch and the main harness. make sure you have continuity.

 

[Jeanric]

Try grounding the Wire that Goes to the Pressure Switch, with the Ignition on.
Of course the Horn, might for be an Overheat

That's exactly what I did in the first place. But ground does not arrive at the horn.

 

[Jeanric]

make sure you are grounding the correct wire. If I recall, there are 2 connectors between the temp switch and the main harness. make sure you have continuity.

Can you share more about these connectors? It's impossible to follow the wires through the harnesses.

 

[Scott Danforth]

Start at the sensor, and worth towards the big cannon plug. Use the schematic as the guide

 

[jimmbo]

That's exactly what I did in the first place. But ground does not arrive at the horn.

Reading your Initial Post, you said you grounded the Sensor, not the Wire going to it