I have a 2001 Honda Accord. The horn won't turn off, and the headlights, turn signals, and tail lights won't stop blinking.

I pulled the horn relay, to stop the horn, and replaced the battery because it was marginal after a charge. The headlights, turn signals, and tail lights still won't stop blinking. The dash lights are fine. If I pull the hazard light fuse the headlights, turn signals, and tail lights still won't stop blinking. The headlight switch, turn signal switch, hazard switch, all seem fine. Car will start. Battery is disconnected for now.

What should I check next?

 

It probably is due to a security/alarm system. What trim level is your car (EX, LX, etc.)?

 

It's an EX.

 

Tthe Accord EX trim level has the factory security system. The security system on an EX is integrated as part of the car's Multiplex Integrated Control Unit (MICU). Many times the cause of the false alarms is due to the security hood switch.

The security hood switch is part of the latch. The way the security hood switch works is when the hood is open, a ground signal is allowed through the switch to the security/multiplex control unit. Normally, when the hood is closed, there should be no ground signal coming from the hood switch. If the hood was closed and the security system sensed a ground signal from the hood switch, it sounds the alarm because it thinks the hood is open.

Try unplugging the connector to the security hood switch to see if it stops the issue you are experiencing. To access the hood switch connector, remove the plastic cover held on with a plastic clip, and you should be able to access all the latch bolts or even the 2P connector without removing the bolts.

 

Plastic cover I am referring to is highlighted in yellow.

 

Thanks.
My plastic cover looks a bit different, and does not seem to expose and wires. (attached 2001HondaAccordEXHood LatchandCover.jpg) They still are fairly inaccessible with the plastic cover detached. There seem to be two. One that mat be related to possibly AC. (attached 2001HondaAccordEXSensorUnderHoodLatch.jpg) The other is a small green connector barely visible directly under the latch assembly itself. (attached 2001HondaAccordEXPossibleSmallGreenHoodAlarmSensor UnderHoodLatch.jpg)

Is the connector the small green one? If so, then it looks like the latch or radiator may need to be removed.

 

Your plastic cover looks identical to what I previously posted. See this other parts diagram for the plastic clips that needs to be removed, so the cover can be removed. After the cover is removed, if you still can't access the hood switch gray connector, then you'll have to remove the latch mounting bolts to more easily get to the connector.

The other connector in your photo is not the the hood switch, that is the outside temperature sensor.

 

Well, I feel like a dummy. I could never get to the plug, because it's on the opposite side between the radiator and the welded crosspiece that the latch attached to, with very little play in the wiring. But with the battery attached, I was able to reset the alarm with the key fob.

Thanks for helping. I learned a lot about these alarms. Haven't had the car for very long. I assumed it would have reset just with the battery disconnected.

 

Good commentary and images... I've learned an awful lot here!