It seems whenever someone asks how to disable DRLs, the topic strays into a debate over whether DRLs are a good idea or not. The tone deteriorates with a bunch of sniping back and forth, and more often than not the original poster never gets a satisfactory answer to his question.
Fact is, DRLs are neither the safety menace the anti-DRL types claim they are, nor the miraculous safety device the pro-DRL types claim they are. The potential safety benefit from DRLs is small, and non-optimal implementations do introduce safety drawbacks that can cancel or reverse the safety benefit. Most arguments against DRLs are actually arguments against the problems caused by particular implementations of DRLs, not against the concept itself.
Headlamp DRLs, both high and low beam, are very common in North America. They are not a good way to do it:
Low beam DRLs make a bulb life issue. Vehicles with headlamp DRLs
usually come factory-equipped with Long Life bulbs. These are very
warranty-friendly and lend themselves to use as DRLs due to their long life, but their output is low and the beam focus (and beam reach) they
produce is relatively short compared to standard bulbs, due to the filament modifications made to get extra long life out of them. For example, the highest-performing version of one particular kind of headlamp bulb produces 1700 lumens over a lifespan of 450 hours, and its filament coil is focused such that the low beam reach is approximately 275 feet. The long-life version of that same kind of headlamp bulb produces 1460 lumens over a lifespan of 1200 hours, and its filament coil focus is such that the low beam reach is approximately 230 feet. Is that 45 feet significant? Probably, given that a great many crashes could've been avoided with just an extra half-second or an extra five feet. Even if we pretend bulbs don't burn out more often with DRL operation of headlamps, this is not a good trade: A small potential increase in daytime safety for a significant decrease in nighttime safety.
And, optically, it's very difficult to have a lamp that serves both as a good low beam and as a good DRL. A good low-beam light pattern is asymmetrical, directing most of the light downward-rightward with only minimal light upward-leftward and towards eye-level leftward angles...but since much of the intended "audience" for a DRL is located in exactly those locations, a well-focused low beam makes an ineffective DRL. A proper DRL puts light in those upward & leftward angles (more exactly, a proper DRL has a symmetrical light pattern in the general shape of a horizontal oval or oblong centered around the DRL's axis). See for example late-model VWs, Mercedes, and various others with halogen projector low beams, these low beam DRLs are practically invisible until general outdoor light levels are low enough that full headlamps (+ tails & markers) are needed.
High beam DRLs are quite common on North American roads, too. They produce a symmetrical beam pattern, but are basically impossible to implement well: If the intensity is high enough that there is a useful amount of light directed to the sides, there is far too much light straight ahead, causing genuine glare problems. If the straight-ahead intensity is reduced enough to control glare properly, the angle of illumination narrows so much that there is essentially no light from the DRL at angles off axis. Because most of the safety benefit from DRLs is in avoiding angle collisions rather than head-ons, this is a problem. There is also the issue of high beam bulb
envelope blackening due to deposited tungsten: halogen headlamp bulbs
operated much below their rated voltage don't self-clean as they do when operated at full power, because the bulb wall temperature doesn't get high enough to initiate and maintain the halogen cycle. So the bulb glass blackens. This condensed tungsten will be cleaned off the bulb and redeposited onto the filament with long enough full-voltage operation of the high beams, but most drivers get to use their high beams only for short periods, so the reduction of their power due to glass blackening is a serious safety performance concern.
Both low and high beam headlamp-based DRLs are so inefficient given the power input and functional output that using them is like opening the refrigerator door and using the fridge light to read a newspaper. System wattage in DRL mode ranges from 60 to 240 watts. The fuel consumption concern is so significant that GM petitioned the US and Canadian governments and won an exemption from the rules requiring Federal fuel economy and emissions type approval tests to be done on vehicles configured exactly the same as the ones that will be sold to the public. The exemption allows them to run the type approval tests with the DRLs disconnected, even though GM will not sell cars without DRLs in the US, and all new vehicles made since 1/1/90 have been required to have DRLs in Canada. H'mmm!
And then we have to look at the way the regulations are written with respect to illumination of a vehicle's parking, tail and marker bulbs with DRLs. Parkers, markers and tails must be illuminated with full-power low-beam DRLs unless the vehicle is equipped with an ambient-light sensor that will turn on the parkers, markers and tails when ambient light levels drop low enough to require the vehicle's conspicuity lights. This presents us with a tough decision:
•Having the parkers, markers and tails on during the day adds between 20
and 84 watts' power consumption to the 60 to 240 watts' power consumption of a headlamp-based DRL system. Now we're looking at between 80 and 324 watts...definitely not trivial in terms of fuel burned and pollution produced.
•Having the taillamps on during the day significantly reduces the visual contrast between the brake lamps being on and their being off. This has been shown to worsen the speed and accuracy with which following drivers react to a vehicle's brake lamps. Safety...?
•And then there are all those extra bulbs that are all going to have shorter effective lives and need replacement sooner, because they're being operated all the time.
OK, so what do we do if we want to have a headlamp-based DRL system, but not run the parkers, markers or tails during the day, and we don't want to install an expensive and troublesome automatic light control? We've got three options permitted by the regulations:
1) Run the low beams at reduced intensity (which aggravates the already poor DRL performance of low beam headlamps as described above)
2) Run the high beams at reduced intensity (which makes DRLs of limited effectiveness and high glare, as described above)
3) Run the high and low beams in series with one another (which makes fairly effective DRLs on some kinds of headlamp systems, but is very fuel inefficient).
And this doesn't even get into the operational problems created by headlamp DRLs. Come up to Canada sometime and see all the people driving around after dark and in bad weather with their DRLs on. Sometimes with their parkers and markers on (in which case they have inadequate forward visibility and with high beam DRLs are creating dangerous levels of glare) and sometimes without their parkers and markers on (in which case they're also invisible from the sides and rear).
The best DRLs are separate, functionally-specific ones that don't do anything else. We don't see a whole lot of these in North America; they're more common in Europe and Scandinavia. In North America, many of the full-size GMC and Chev trucks and SUVs have this kind of DRL, and some late-model Nissan Maximas, and the newest BMWs (which now have extra-bright operation of their "angel eye" rings around the headlamp optics...those were formerly just parking lamps).
The second best system is the full-time operation of the front turn signals (except when they are blinking as signals). Dedicated DRLs and front turn signals give a light distribution with a viewing angle, no glare, they don't cast enough light forward to fool the driver into driving with just DRLs after dark, they tend to use bulbs that consume a lot less power (=fuel) than headlight bulbs and have a much longer life. In Canada and/or the USA, many recent Cadillacs, Chevrolet/GMC large vans and minivans, the last two generations of Chevrolet Corvette, some Toyota and Lexus models, the Lincoln MKZ and assorted other vehicles use the turn signal DRLs. You can get aftermarket modules ranging from reasonably- to unreasonably-priced to implement this kind of DRL operation on a vehicle not originally equipped.
Parking lamps do not work effectively as DRLs. They are not bright enough.
As far as the original poster's question: How to disable the DRLs, and how difficult it will be, depends on how they are wired up. Sometimes it's as simple as pulling a fuse or relay, unplugging a DRL module, or grounding a wire leading to the DRL module. Sometimes it's a great deal more complicated than that, as for example in most GM passenger cars built in the last five or six years. The "one click of the parking brake" trick hasn't worked for years — you get about 5 feet before the chime starts bonging and the computer turns the DRLs back on. And sometimes the DRL circuitry is so deeply integrated into the headlamp circuitry that it's essentially impossible to deactivate the DRLs without screwing up the normal nighttime operation of the headlamps.
Your best bet is to get hold of a wiring diagram for your specific make, model, and year and study it to see how the DRLs are wired in. From there, it is often obvious how to disable them (or at least it gives you a starting point from which to ask for more help).
