Wiring & Wiring Harnesses

Wiring a headlight retrofit setup can seem daunting. There are a lot of aspects to controlling the HID system and ensuring your vehicle’s wiring is safe.

A wiring harness is designed to draw power directly from the vehicle’s battery. This is done through the use of an inline fused relay box. A bi-xenon wiring harness as well as a standalone bi-xenon control box, also have built-in diodes to keep power supplied to the HID ballast at all times during high & low beam operation.

Bi-Xenon Harness: This is a full harness with built in diodes, smart circuits and relays to control what was normally a high/low beam headlight from the factory that is now a bi-xenon headlight projector retrofit. Morimoto Motocontrol Bi-xenon Harness





Standalone Harness: This is a compact NO-relay harness/control box setup with built in diodes & smart circuits to control what was normally a high/low beam headlight from the factory that is now a bi-xenon headlight projector retrofit. (this is a compact setup with one control box PER side on the vehicle – great for snug setups or headlights with OEM plugs such as Mini Coopers and VW’s)Morimoto Standalone Harness/Control Boxes




Low Beam: A low beam harness is very straight forward. This is a simple fused and relayed wiring harness that turns on with a low beam circuit. This can be used in low beam only projector headlight retrofits, a quad projector retrofit (to power a 2nd set of ballasts) or to power ballasts for a bi-xenon setup where the high beam circuit is normally separate from the low beam (most dual bulb headlights).Morimoto Low Beam Wiring Harness

A common issue is whether or not to actually use a wiring harness. It’s always recommended that a wiring harness be used when upgrading to a headlight  retrofit setup, but is it really required? The answer depends on your system components & setup.

If, for example, you are utilizing generic no-name brand ballasts, a wiring harness is a must. The reason behind this is that generic ballasts have unreliable voltage requirements. More often than not they draw too much current upon startup, spike during operation and can fluctuate & while the bulb is on. This can damage your factory halogen wiring.

If you’re using higher quality OEM ballasts OR reputable aftermarket ballasts, a wiring harness is ultimately up to your discretion (or your retrofitter’s). A variety of vehicles come with HIDs from the factory and they are already setup to meet the electrical requirements of an HID ballast. If you are upgrading to a projector retrofit on one of these vehicles, a wiring harness is not needed.

The same could be said for a non-HID equipped vehicle as long as high quality ballasts are being used (such as OEM spec ballasts or an All Digital Morimoto ballast).

A good quality ballast (such as an OEM spec or an All Digital Morimoto) will very briefly use a higher current draw during startup (nominal at around 9-10 amps for about 1/5th of a second) and settle at 3-4 amps during the bulb’s on cycle. This situation generally doesn’t require a wiring harness setup.

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