Anatomy of a Retrofit

Anatomy of a Retrofit

Retrofit headlights look great and provide a massive upgrade in lighting, but with no prior knowledge it's difficult to know what everything is and how everything works. We'll go through the major components of a projector retrofit, but if you have any questions about specific details, other add ons, or want further clarification, feel free to send us an email at


The first thing you're going to want to find out is what type of headlights you have. For example, if you have H4 headlights, you have both high and low beams in a single area within your housing. Or, if you have 9005/9006 headlights, you have separate high and low beams. While these are not the only types of headlight bulbs, they are the two different setups. This information will come into play below.


The size of a projector refers to the lens diameter. A full size projector has a 3 inch lens, while a "mini" projector has a diameter of 2.5 inches. 

ACME HID Projectors (2.5in lens)

Most Toyota housings have space for a full size projector (and shroud, which we will get to shortly). Sedans, compact SUV's and some truck models only have space for a mini projector and shroud. 

The light output from a mini projector vs a full size projector of the same type, for example a mini HID projector vs a full size HID projector, will be very similar. The mini projector's output will cover a slightly smaller area than a full size projector. 


A HID (High Intensity Discharge) bulb works by passing an electric current through a cylinder filled with xenon gas. These projectors require a bulb to operate. HID bulbs come in a variety of temperatures (often called tints), measured in Kelvins (K). A comparison of the different temperatures is shown below. HID projectors are the standard option on most projector retrofits. 

These headlights take a second to start up and require a ballast, which regulates the electricity to the bulb. They're needed because HID headlights require a lot of power to start up and less power once started. 

The other required wiring component is a wiring harness. These harnesses will plug directly into your factory headlight plug and make install a breeze. Simply connect the harness to the ballasts and bulbs, a power source, and ground everything. As can be seen below, some of the components are housed in a box as well. When combined with the boxes required for the ballast, your engine bay can begin to get pretty cluttered, pretty fast. This is avoidable with LED projectors, however. 

Morimoto Wiring Harness

The other common projector type are LED projectors. The explanation as to how these work is a bit complicated, so we'll just accept that they work and move on. LED projectors do not require a bulb and are brighter than HID projectors. They emit a white light, generally around 5000k-6000k. LED headlights start up instantly and plug right into the factory connector once you pin the correct wires into the correct male connector. Vehicles with H4 headlights (both hi and lo beam in one spot) will require a wiring harness that plugs into the factory headlight connector and controls both the driver and passenger headlights. 

Dedicated High-Beam Projectors/Quad Projectors

Many vehicles do not have both the high and low beam in a single location with the headlight. For these vehicles, retrofits are a little bit different. Your standard projector will be retrofitted into the low beam spot and is still able to function as the hi beam. However, there is the additional option to add a high beam projector or a mini projector in the high beam spot. 

The high beam projector, shown below, acts as a bolster to the LED/HID projectors high beam, providing a focused beam pattern quite far down the road. The high beam projector is also backlit and can function as a daytime running light (shown in the picture at the beginning of the article). The newly released 2.0 version also comes with an RGB option. 

By putting a mini projector in the hi beam spot, you're able to have 4 low and 4 hi beams- a true quad projector setup. Though it can get quite expensive, this setup is extremely bright. 


Now to the fun stuff! Halos are small rings of light that can be added to a headlight build to create unique designs. Standard halos are switchback halos, which have separate wires for white and amber light. The most common application for these is using the white as a daytime running light and the amber as a turn signal, but there's plenty of other possibilities. 

Halos are responsible for creating the backlit look in the area around the projector. Some shrouds require them and others will function without them. This will explained further in the shrouds section. 


An RGB upgrade to halos allows the halos to be light up virtually any color in the spectrum. From most retrofitters, these halos will come with a bluetooth controller to control the halos from your phone. You have the ability to lock them as a single color, including white, which is helpful for daytime running lights. 

RGB halos also include the switchback function as well. 

Neopixel RGB halos by BxBuilt take it one step further. These halos are engineered to allow sections of the halos to light up certain colors, rather than the entire halo at once. They're absolutely stunning in "show" mode, check an example out here! 

We're proud to carry these standard on all RGB builds. 


Shrouds do what the name suggests and shroud the inside of the projector from view, creating a much cleaner look. They come in a variety of designs and sizes. Mini shrouds are used for smaller applications and can only be used with 2.5 inch projectors. Most mini shrouds are not able to support a rear halo due to space constraints, but all can still include a front halo. 

Full size shrouds can accommodate both 2.5 inch (with an adapter ring) and 3 inch projectors. A guide to the various shrouds is shown below. 


So for a complete retrofit, you need to pick your projector type and size, based on your vehicle. If you have smaller headlight housings, you're probably going to need 2.5 in projectors. If you have larger housings, you'd be able to get away with a full size projector. Just pick your shroud and decide if you want to add halos. If you want to add halos, you have to decide if you want those halos to be RGB. 

Hopefully this article made it a lot easier to understand the terminology and options associated with a projector retrofit. If you have any questions, we are always available to assist via email!