Vauxall Astra N reg (95) HELP please car horn is draining battery

Strider590

Lum wrote: »

These are a little bit more involved to wire up but they worked fine, passed several MOTs and once caused a taxi driver to crash into a central reservation fence after I beeped it in response to his drifting across the lane divider toward the side of my car.

Now seeing the value in converting to air horns.......

Lum

It really was funny as hell having them on a manky shed L reg diesel Passat estate with gaffer tape all over it holding various bits on. Not as funny as the death glare I got from an M3 driver as I overtook him (and the lorry he was tailgating) on a single carriageway, with streams of gaffer tape rattling in the wind as they slowly peeled off my leaky sunroof.

I still miss that car, it's been one of the best cheap sheds I ever owned and that umwelt diesel engine is utterly bulletproof.

shaun_from_Africa

If the car has an alarm fitted, there is one other thing that you could try.

Connect the horn up again and leave the car overnight but don't lock it up. (providing that you have somewhere secure to leave it).

An awful lot of cars have the horn wired into the alarm circuit as they use the horn for the main sounder when the vehicle is broken into.
Once the alarm has been set (either by locking the car or using a remote), there could be a faulty relay or alarm module causing a slight current leak into the horn circuit.

pendulum

I think what I'd do before buying a new horn is connect a 12v bulb to the horn circuit instead of the horn
If that still drains the battery then you will know it's not the horn, and it doesn't cost anything to try that out, and only takes 5 minutes.

But thinking about it, how could a faulty horn cause this? It can't can it? If the switch is off, the horn shouldn't get any power, and it can't draw power if it can't possibly get any...

So I doubt it's the horn itself but would still check as it costs nothing...

Could get handy with a multimeter and measure the current with the alarm on and off (as mentioned with the above post) along with removing fuses for other circuits etc and see if any other circuit has an effect on the current draw by the horn circuit

Failing that (and swapping the relay as mentioned above) I guess it's time to get the electrical diagrams out, I wouldn't know where to start with those though, spaghetti junction

Joe_Horner

It won't be the horn itself. For the horn to draw current it needs a supply and an earth (ie: a complete circuit). That circuit should only be complete when you push the button or, as Shaun suggested, the alarm tries to sound it.

Horns are generally wired up with a constant feed and the switch (either button or electronic through the alarm) to earth so, if it's drawing current all on its own, the fault will be somewhere in that earth wiring / switching. Unfortunately, it's unlikely to be either the wiring or the switch because the chance of getting a short to earth that's reliable enough to drain the battery, while still being too high resistance to make any sound, is pretty small. Which makes the most likely candidate the alarm (possibly built into the ECU but may be separate and / or aftermarket at that age).

If it IS that then a simple (and cheap) solution is to disconnect the alarm if it's separate, or change the permanent live feed to one that's ignition switched if it's integral with the ECU. That means that your alarm won't sound any more but will make it impossible for it to drain the battery, while leaving it working for MOT purposes (it doesn't have to work with the ignition off)

Delivery_Driver

Horn is most likely a permanent live so maybe someone tapped into it for that and shared it's earth.Have seen stereos put on a permanent live before so can be listened to without leaving the keys in the ignition.

Joe_Horner

True, but if it was something else draining on the same feed then having the horn plugged in or not (at the horn) would make no difference.

The fact it only drains when it's plugged in means that whatever's allowing current to flow is "downstream" towards earth, which wouldn't work for accessory wiring.

s_b

on an astra this age we have
battery
positive feed to horn
feed then going to horn push
earthing on steering column when horn sounded

so as said there is something else attached to this permanent live to the horn push
i too would suggest its an aftermarket immobilisor with lets say a leak fault and it needs chopping out
only problem is it will also be wired possibly to cutting the fuel pump relay supply and also coil output so a little bit more involved than at first glance
a good auto electrician would have it out in an easy hour though as could i

needs doing because it could cause a fire

motorguy

Horseunderwater wrote: »

Just buy a whole new horn and some new wiring to thread through. Fiddly but cheapish on the whole. Once all re wired and replaced, hopefully will work fine.

+1

I've just had a car traded in with this done. The button is labelled 'HORN' and i think thats enough for it to pass MOT like that.

Lum

pgilc1 wrote: »

I've just had a car traded in with this done. The button is labelled 'HORN' and i think thats enough for it to pass MOT like that.

It is. I did the same thing on my old Escort, but mainly because the default horn button in the centre of my steering wheel had become loose and over-sensitive, so I'd often end up knocking it while reversing.

I did try to do a nice job though. I got the plastic surround from a higher spec Escort that was fitted with front foglights so that I had an extra button to wire up that looked like it was supposed to be there. A bit of black tape over the original horn symbol, and then attach the new button with some tippex and some questionable artwork with a black felt tip pen and it was all done.