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Battery drain on horn/brake light circuit

12-11-2010, 07:02 PM
My voltmeter reads .392-.40 and when I pull the 15 amp fuse for the horn/brake light circuit under the hood it reads .013-.014.

If I leave the fuse in and don't drive my car the next day, the battery will be dead. Disconnecting the brake light switch and also the horn at the steering wheel doesn't change anything.

Any ideas? Any specifics on what route the wiring takes between the fuse box under the hood and the brake pedal?

02-20-2011, 12:01 AM
don't know if you are still looking for an answer ... did you try disconnecting the brake switch under he pedal ? It may also have a relay that is "leaking"

02-20-2011, 12:09 AM
I actually did try that too. No change. I carry a fuse puller in my pocket and have been poppin' the hood and pulling the fuse when I'm done driving the car for the day. Kind of annoying.

I could just put a switch on that circuit, but then I still haven't fixed the problem. (I'm a bit OC)

I may investigate the horn switch some more. Sometimes the horn don't work, almost like it's not getting good contact when I push it. Of course when I take it apart, it all looks good.

We wouldn't develop loving relationships with our cars if they never screwed us.:iceslolan

02-20-2011, 04:23 PM
the horn has a relay, try pulling that and see what the current draw is. Just out of curiosity, do you have an aftermarket alarm ?

02-22-2011, 01:09 AM
Where is the horn relay? I have disconnected the horn at the steering wheel and at each of the horns behind the bumper and get no drop on the voltmeter. I also disconnected the brake lights and the switch at the pedal. I pulled each fuse under the dash and under the hood one at a time with no effect. The only fuse that changed the reading was the 15amp fuse under the hood for the brake light and horn circuit.

I do have an aftermarket alarm. It doesn't work right now. I have considered this as a culprit, but have ruled it out because I don't see a link between the two that looks problematic. It's possible that I've overlooked something though.

02-22-2011, 06:00 AM
Try the brake switch at the emergency brake handle and try to remove both the ground and positive from your alarm.

02-22-2011, 04:54 PM
there is a relay either under the dash or under the hood for the horn can't remember which. The alarm can sometimes have auto-start that may be tied into the brake switch. Just because the alarm is disbled does NOT mean it's harness is not still wired up - try pulling the harness(es) out of the brain box to see what happens.

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