Rep Power: 0

I had recently replaced a heater core on a 05 civic and now the horn won’t stop blowing when the engine is off or on idle

 
Rep Power: 126

Start tracing back wires. It's probably shorting on something near where you were working

 
Rep Power: 224

Horn relay switch wire would run through firewall in the body harness which is around the heater core. You may have cut or pinched the harness. Unplug the horn or pull the relay in the under-hood box to get it to stop. FYI, pulling the relay will also disable cruise control.

 
Rep Power: 0

I really won’t know what to look for.

 
Rep Power: 0

it may be pinched since I took the dash out and unplugged the wire harness to replace the heater core and o kinda didn’t know how the wire went so I did the best I could

 
Rep Power: 224

How would you like to remove the heater core again? You will need to go back in to check your work and verify the harness isn't damaged.

When pushed the horn pad in the steering wheel provides a ground to the horn relay in the under-hood fuse box. If this wire were pinched or cut it could very easily be shorted to the chassis somewhere causing the horn to always be on.

 
Rep Power: 0

I already replaced the heater core. I went back into the car the other day to se if the wired was cut or pinched and they looked well.

 
Rep Power: 224

Remove the relay and verify the coil side is constantly grounded. If so, find why it's grounded. The wire would run from the under-hood fuse/relay box through the firewall (suspiciously close to where you were working) and up to the horn pad in the steering wheel.

Besides a damaged wire/harness from the heater core replacement the relay could be failing or the horn pad stuck on.

 
Rep Power: 0

I’m going to check the wiring later as far as the horn pad I’m not sure if it stuck I’ve put it on three to four times already and it seems like normal. I’m going to turn the car on and press the horn or wiggle the wheel to test it.

 
Rep Power: 0

Update so I figured it out and it was just a wire put in the wrong outlet. Now I’m havibn windows that won’t go down which is probably the same problem.

 
Rep Power: 367

windows are usually tied to broken wires at the door hinges.
check that first

how did the connector end in the wrong outlet?!?