Rich,

That could cause the horn to blow. Look at the seatbelt where it mounts to the seat and see if it has a wire coming out of it. If so, then there is a switch inside the belt coupling.

Does the seat belt happen to cause the horn to blow?

Rich,

Since you state the horn is blowing every three seconds, suspect either a low fuel sensor is sensing the tank is getting low or a specific alarm is wired into the horn. Should this be the case, will need serial number to identify which alarm is wired into the horn. If the horn is actually going off randomly, need to check a few connections. Find where the horn wires come up through the steer column. Unplug the connector at the bottom of the column and see if the horn still blows. Make sure the coolant level sensor is not leaking into the connector. If it is, this can cause the horn to blow. You can also disconnect connectors CPS4 and 17. If the horn stops blowing, check light harness for shorts. Good Luck.