The DRL 2005 SE was designed to 'command and control' the dual filament turn signal bulb like no product ever invented. It does this with its internal QuadControl circuitry - the product can actually automatically control 4 different lighting 'zones' at one time.  First the 'Why', and then the 'How'.

Some estimates say that 60 to 80% of all the vehicles in the world have a dual filament front turn signal system. This the exception to this rule is in Europe, where front parking lights must be white, and turn signals must be amber - hence 2 different bulbs per side are needed (2 white parking lamps and 2 amber signaling lamps).

In the US, front parking lights can be white or amber, but turn signals must be amber.  From the early 1960's until the late 1980's, almost all US domestic vehicles have had amber parking lights and amber turn signals, all taken care of by the dual filament front turn signal bulb (one for right, and one for left, of course).


For the dual filament front turn signal system, there is a 27-28 watt turn signal bulb filament and a 7-8 watt parking light filament (In contrast, European turn signal bulbs are typically 21 watt [and single filament]).

The 28 watt front turn signal bulb filament before 1990 and Canadian DRLs came along was always a pulse only device - day or night, the duty cycle of this bulb was normally pulsing a 1 second on-off intervals, with the signaling lamp being lit 60% to 75% of that time (as per SAE J590 October 1965)

In contrast, the 8 watt parking light filament is a constant 'on' lamp, but only at night (when the lights are turned on).

As per US code, the turn signal lamp must be at least 2.5 times brighter in output than the parking light output. This is so the turn signal will overpower the parking light at night, making sure the turn signals are seen over and above the parking lights themselves.

In the dual filament '2 bulbs in 1' case, a 28 watt bulb filament is 3.5 times brighter than its 8 watt parking light 'bulb-mate' [28/8=3.5]. The brightest filament is pulse only , and the dimmer filament is constant on at night.


Strictly from a common sense and engineering viewpoint, the dual filament turn signal bulb filament can never be used as a constant on at the same time the parking light filament is constant on.

First, the turn signal filament is so much brighter than the parking light filament, the parking light filament itself can add no 'extra' or additional light output to the mix while the turn signal filament is activated constant on [its 2/3rds dimmer light is eclisped by the brighter turn signal filament].

Second, since the parking light filament can not contribute any 'extra' light to the output when the turn signal bulb is constant 'on', the only thing it can add is unnecessary heat.

Quad control features built-in the DRL-2005 SE control heat from the parking filament selectively, but in the case of the dual filament turn signal bulb only. They offer this engineering-based control in only 2 very specific cases: 1) only when the Turn DRLs are on, and 2) only at night (which is when the parking light filaments are on). 

This is only for dual filament front signal light setups combined with the SE night function module; all other 'split bulb' euro-type and US import vehicles are not wired to take advantage of this engineered control system.

To understand just how the DRL-2005 SE works, take a closer look at the SE operational flow chart below:

DRL-2005 SE Daytime+'Parking Light/Night Mode' function operational flowchart

(click on graphic to enlarge)