Ok, so my buddy has an 03 wrx and recently the battery went on him so he got a new one put it in and now as soon as you connect it the horn goes on and just stays on. not intermittent just stays on unless you pull the fuse or relay. Also there is no power anywhere. no interior lights, nothing happens with the key no door locks, windows, no security light or gauges at all for that matter. Tried the key thing on and off 3 times with no luck and tried the keyless entry nothing will shut this horn off. I am going to go through the wiring diagrams myself to try and trace the source, but does anyone have experience with something like this. I really dont think its security related, but the car is completely dead. The only thing that works is the little switch on the steering column that turns the parking lights on


All fuses look good??

I think there is two possible problems with this trouble. Either the horn switch is shorted or the horn relay is stuck.

The power problem should be pretty easy to find by using a test light probe to check where power is getting to. There may be a problem in the power panel under the hood. The problem may be with the ignition switch or the connector to it also.

or you connected the cables to the wrong posts, and blew the 80amp fuse protecting your car's circuits