66 dart electrical problems

You may have a / some harness wires crossed if the horn fires off the TS switch.

Here's what I'd do......

1......Check the brake light switch is "cold" that is not somehow activated

2.......Remove both flashers from their sockets

The above two steps should remove all power coming "to" the TS switch

The only thing left is the horn, as power goes to one end of the horn relay coil, and the other end normally goes to the horn button, grounding to activate.

If it's hooked to the wrong harness terminal, you could get what's going on there.