Voltage drop

when I turn the ignistion on the battery light on the dash is on, then when i fire the car up and tap the accelerator the battery light goes out.

I noticed the other day if  I try the horn before the battery light goes out, all I hear is the relay clicking and not the actual horn, but as soon as the battery light goes out, the horn works????

can any help?

Cheers

Think its as the horn draws quite a bit of voltage from battery(Esp if its a twin horn), so when the battery isnt charging ie before you blip the accelerator its voltage is too low, could be totally wrong though dude lol

its a single horn!  want to fit a twin but must fix this problem first!!  I should really check and clean up any bad earths. I'm hoping this might cure it, but maybe it's something else?????

andy is right, mine is the same. engine off the relay clicks and horns make no sound, engine on and they work.  try cleaning up the contacts on the horn

Sounds like the battery voltage is a bit low. Would expect it to be over 12 volts idle and over 14 volts with the engine running. The alternator is pushing up the battery voltage with the engine running.

Don't think it is a voltage drop problem it is  the same wiring from battery to horn circuit with engine running or not.

Keep smiling J.

this is true, but sometimes the horns need more than 12v to work. also you need to account for voltage loss thru 20+ year old wiring, so the horns may not be seeing the full 12v at the plug

as i say, mine are the same. i know my battery is healthy as i have checked it, just my horns need the engine to be running for them to sound.  I just havent bothered to look into it, since they work fine and I have other problems that are more pressing  

just found this, I know it's dredging an old topic up.

When i first got the golf and went to fit the air horns i had lying around, they wouldn't work. the pump span but no noise.  direct on the battery they worked!!!

I checked the voltage at the horn cables and with the button pushed (engine off) i had 11.8v.  engine on i had 12.4.  Battery read 12.7 stood still!!!

i had a massive voltage drop across the loom, so i fitted a relay and the horns are fine now!!!  I'm guessing they needed 12.7ish to run but weren't getting enough.

My mate had the same problem in her jetta.  Relay cured it.

Jon.

relay will cure it but it's not neccersery, the problem is old wiring, which can (and should) be replaced as fire and cars dont mix well.

Madferret said

relay will cure it but it's not neccersery, the problem is old wiring, which can (and should) be replaced as fire and cars dont mix well.

how do i fix this then without fitting a relay :dontknow:
i thought that i'd only need to replace a wire if its actually damaged (i'm yet to do a continuity test but will let you know)
can it be that all related terminals and earths are brushed clean and maybe cure it that way???… without replacing the wire?

As time goes on the wire itself gets corroded and sometimes just turns to powder (usually external wiring with water ingress) so just replace the wires and sockets/pins.  :wink: