I have a 2003 g35 infiniti sedan (175k) - yesterday while i was driving on a straight road the horn intermittently started to blow on its own about 3 times (short intervals).
About an 30 mins after i parked, the horn just stayed on constantly. Tried unlock with the keyfob to disable but no dice. Disconnected the battery terminal before my neighbors killed me. Waited a few mins but same issue resumed when reconnecting terminal. Decided to pull the horn relay and obvious now its quiet. Any have an idea what the cause could be? Thanks in advance.

 

First, get a simple 12v test light, unplug the horn and connect the test light to the contacts, that way you're not pissing anyone off during testing.

Could be the relay itself. Swap it with another relay and see if the problem persists. If it does, check out the steering wheel, could be contacts stuck down.

 

Thanks!- will def check that and update with results.