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  • Added on: Aug 30 2016 06:56 AM
  • Views: 4277
  • Time needed: 2 hours

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How To: Upgrade “headlights left on” warning buzzer

This tutorial explains how to construct and install a "headlights left on" warning buzzer upgrade.

Posted by Dust Buster on Aug 30 2016 06:56 AM

1 x 10mAmp 12V piezo (piezoelectric) buzzer (₤0.47 to ₤2.43),
2 x 10 Amps (10A) 12V mini fuse (₤0.08 to ₤0.12 each) (1 for option one, 2 for option two),
2 x 5 Amps (5A) 12V mini fuse (₤0.08 to ₤0.12 each) (second optional, but recommended),
2 x diodes for option two (₤0.06 each)
6 x tiny (conductive, ferrous) screws,
Heat shrink wrap or electrical tape,
Soldering (rod),
Flux (if not in the soldering rod),
Short length of flex / wire (optional) and
Short length of double-sided tape

Total: ₤0.91 to ₤2.99 plus incidentals


Wire strippers,
Drill with tiny bit,
Soldering iron,
Continuity tester and
Wire cutter

Time: 2 hours
Difficulty: 1.5 out of 5

I don’t know about you, but to me the loudness of the “headlights left on” warning buzzer is too quiet / soft. Let’s just say that on more than one occasion I have left my headlights on when disembarking. When I asked the dealership if they could isolate the wire for me, they just laughed saying they knew it was a common complaint.

So, the vehicle is still under warranty. I want an effective, but cheap, easily removable solution. Google helped by pointing me to piezo buzzers. They work by passing electricity in one direction only, like a diode. This solution does not require a relay. So, we need to connect the buzzer between the ignition switched output and the headlights. To ensure the correct polarity, switch on the headlights without the ignition being on and it should buzz. If not, reverse the wiring. A continuity tester uses a small current to test resistance, but gives a false buzzer sound across the piezo.

The one-way effect works like this. When both the ignition and lights are on the buzzer will have 12V on both sides, will not pass current and will not buzz. With the ignition on, but not the headlights, the buzzer will have 12V on the one side. However, this is the wrong side and therefore, will not buzz. With the lights on, but ignition off, the buzzer will have 12V from the correct side and will buzz.

Visit your local electronics store rather than ordering online. Why? You can listen to the device and get them to reverse the polarity to prove to yourself that it won’t work in the opposite direction. If you are older, you probably have a “dip/s” in your auditory range. Listening to the different buzzers will help determine which is best for you. Hearing depends upon frequency (Hz) and volume (dB – decibels – logarithmic scale). I’ve seen “in shop” buzzers that range from 2700 Hz to 6600 Hz and from 75 dB (loud conversation) to 115 dB (rock concert) with 90 to 95 dB of sustained exposure probably resulting in hearing loss. What is important is that it can work with 12 Volts and is rated at 10mA (milli-Amps). The 10mA is important as this is the amount that will “leak” back into the lower resistance circuits which become the “ground” for the buzzer. This will also protect the integrity of the electrical system. You could probably leave this buzzer sounding for a week and not drain the battery due to this small current draw. Smaller is better (2mA vs 10mA), but may be quieter.

Most people switch off their ignition from low beams rather than from high beams...but, I could be wrong. Thus, there are two options. If you are convinced that you will only leave on your dipped headlights, then choose option one.
If you think that you may leave the headlights on in either dipped or bright, then choose option two. The difference is that option two requires the two diodes. Diodes are like one-way valves. When the dipped right-hand headlight (RH Dipped) is on, you don’t want it to power the left-hand bright headlight (LH Headlt) and vice versa. The diodes will prevent this, but due to their internal resistance, they will make the buzzer softer. Mine is rated at 96 dB. So, somewhat quieter was in order. The trouble is, I don’t know what size diode to tell you to get. A quick calculation at the electronics shop was incorrect yielding 3 Amp, 1kV. This had too much resistance for option two to work for me….for now. As each mode (dipped, bright) and each headlight has a fuse, possibly dividing by four would be a good start.
So, let’s get started.

Option One: Metal pokes through the top of the fuses, but is insufficient for anchoring a lead. Drill a tiny hole next to the metal into the plastic of one fuse to give the tiny screw some bite. Do the same for the other fuse. If the buzzer didn’t come prepped for installation, strip back some insulation. Hand twist the bare wire of one end of the buzzer to one 10A fuse and the other wire of the buzzer to the 5A fuse. Insulate both. Now you are ready to “test” that the polarity is correct before soldering.
Why the double 5A in series? Well, I couldn’t measure the direction of electricity flow to make sure that the current coming from the 10A side would correctly go through the 5A fuse to protect the instrument panel. So, belts and braces and optional for you, I used two 5A fuses. BTW, the instrument panel does not light up when the buzzer goes off. So, it is finding earth elsewhere, probably towards the ignition switch. Most everything else in the fuse box is greater than 5A. So, all should be good, especially as only 10mA is seeking ground.

Option Two: Drill next to the protruding metal post of all three fuses (four if you double 5A like above). You will probably want to cut (and bend) the long very stiff leads on either side of the diodes to a more manageable length and to ensure you can close the fuse cover. You want current to flow from the fuse through the diode (and not the other way). A continuity tester set to resistance will show which way to insert the diode next to the screw for soldering (as it works one way, but not the other). Both 10A fuses will need a diode each. The diodes need to be wired together. Most any short length of flex / wire will do, failing which the buzzer has sufficient length leads to shorten one for this purpose. You want to insert the wire between the diodes to make installation of the fuses easier. That is, one at a time.
Open the cabin’s Fuse Box Cover by pulling from the bottom. On RHD (right hand drive) vehicles, this fuse box can be found by opening the Co-Pilot’s / shotgun’s door.
Yikes! That’s a lot of fuses.
Unless you like looking up each symbol… BTW – this is a good place to store the removed fuses so that you know where they are stored for removing during dealership visits.
…then this might be more useful.
Both Options: Remove the 5A Fuse from the Instrument Panel slot using the tweezers provided on the back of the cabin’s Fuse Box Cover, unless you have very thin fingers. Also, remove the 10A RH (Right Hand) Dipped Headlight fuse (and LH Headlt for Option Two). Insert the modified fuses appropriately with the piezo. Make sure that the two buzzer leads do not contact one another. Turn the ignition key to “on” to get the Instrument Panel to light up. If the buzzer sounds now, switch off the ignition; reverse the buzzer wires and try again.

Both Options: With the ignition “on” and no sound, switch on the headlights. There should also be no sound now. Now switch off the ignition with the headlights still on and the buzzer should sound. Switch off the headlights. Remove your modified fuses with the temporary wiring and make the connections more permanent with solder wrapped with either heat shrink wrap or electrical tape. Re-install and replace the Fuse Box Cover. If you need to take your vehicle back to the dealership, just uninstall. Oh! I attached the piezo with double-sided tape to prevent it banging around.

My thinking on the choice of which fuses to modify is based on the Instrument Panel being the one circuit that I thought would satisfice (I didn’t try any others) for the ignition switched output. For the headlights, I just chose the nearest headlight fuses, being the RH Dipped (and LH Headlt for Option Two).
PS: If the whole Instrument Panel only uses a 5A fuse and if this is what is doing the “headlights left on” detection and providing the warning buzzer, then no WONDER it is too quiet.

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