4.5 Inch Motorcycle Auxiliary Lights (PAR36): Fitment & Wiring
A practical reference for riders replacing passing lamps, fog lights and auxiliary lights on cruisers and touring motorcycles.
Quick answers
- PAR36 means 4.5 inches. The number is the diameter in eighths of an inch: 36 ÷ 8 = 4.5 in, or 114.3 mm.
- Three wiring types exist. Motorcycle 4.5 inch lamps use an 881 bulb, an H3 bulb, or a one-piece sealed beam. Model year decides which.
- Spot beam for road riding. Flood beam spreads wide and short, and causes glare for oncoming traffic when aimed level.
- Depth decides factory-bucket fitment. Typical LED lamps run 40–50 mm deep. Measure your housing before ordering.
- 18W LED beats 27W halogen. A quality 18W unit produces roughly 1,300 effective lumens versus about 800–900 for a factory 881 halogen.
- IP66 is sufficient for road use. The extra protection in IP67 covers immersion, which a passing lamp never experiences.
What is a PAR36 lamp?
A PAR36 lamp is a round lighting unit measuring 4.5 inches (114.3 mm) in diameter. PAR stands for Parabolic Aluminized Reflector, and the number expresses the diameter in eighths of an inch — so PAR36 is 36 ÷ 8 = 4.5 inches. The same standard appears on motorcycles, tractors, forklifts, and aircraft landing gear.
On motorcycles, 4.5 inch lamps are used as passing lamps (also called auxiliary lights, driving lights, or fog lights) mounted either side of the main 7 inch headlight. This three-lamp arrangement is standard on American-style cruisers and touring bikes.
One caution: the diameter is standardized, but almost nothing else is. Two lamps that both measure 4.5 inches can differ in depth, terminal type, beam pattern and lens material — and any one of those can stop an install.
Which motorcycles use 4.5 inch auxiliary lights?
4.5 inch auxiliary lamps are used by Harley-Davidson touring and Softail models, Indian touring models, and most Japanese heavyweight cruisers fitted with a passing light kit or aftermarket light bar.
Bikes without factory passing lamps — Street Glide (FLHX), Fat Boy, Softail Slim, and most metric cruisers — still use 4.5 inch lamps once an aftermarket light bar or fork bracket is fitted. That is the most common install of all.
Factory bucket or light bar? Identify this first
The mounting method determines which fitment constraints apply to you. A factory lamp bucket encloses the lamp and limits both depth and diameter; a light bar or bracket mount does neither.
If you are mounting on a bar or bracket, most fitment questions in this guide do not apply. Choose a beam pattern, choose a terminal type, and wire it up.
What wiring does my passing lamp use?
Motorcycle 4.5 inch auxiliary lamps use one of three connections: an 881 bulb, an H3 bulb, or a one-piece sealed beam with rear terminals. Later Harley touring models generally use 881 bulbs; bikes from roughly the mid-2000s and earlier typically use H3 bulbs or sealed beams. This is the single most common source of returns in the category.
Two-minute check before ordering. Remove the trim ring from one lamp and look at the back. If a bulb pulls out, note its base shape. If the lens and reflector are one piece, you need a sealed beam. Photograph the connector — you will want that photo when comparing products.
Screw terminals or a pigtail lead?
Sealed beam replacements come with either threaded posts on the rear housing or a short pre-attached wire lead. Screw terminals accept ring or spade connectors directly, stay serviceable, and suit custom harnesses. A pigtail is faster to fit and keeps the joint sealed away from road spray.
Be clear that a pigtail is a bare lead, not a factory plug. If your bike currently runs an 881 or H3 bulb, a sealed beam unit replaces the whole assembly and you will be joining wires rather than clicking a connector together. Sort the adapter, crimps and heat-shrink out before the first screw comes off — this is the step that turns a twenty-minute job into a weekend one.
Original halogen left, LED right. The colour difference is why most riders replace both lamps at once.
Should motorcycle auxiliary lights be spot or flood?
Spot beam is the correct choice for street riding. A spot beam concentrates light into a narrow, long-reaching column that extends how far ahead you can read the road. A flood beam spreads light wide and short, which suits slow-speed and off-road use but throws light across the centre line at highway speed.
Riders who split their time between highway and slow technical riding sometimes run one spot and one flood — reach on one side, peripheral fill on the other. What causes problems is ending up with flood beams by accident, then aiming them level.
Why won't my 4.5 inch LED fit the housing?
The two causes are depth and actual diameter. A lamp can be exactly 4.5 inches across and still fail to fit a factory bucket.
Depth behind the lens
LED lamps carry a heat sink and driver behind the lens, and typically measure 40–50 mm from lens face to rear. Older factory buckets are shallow enough that this becomes the deciding factor. Measure the usable depth inside your housing from the lens seat to the back wall, then compare it against the lamp's published height. If a product page does not state a depth figure, ask before buying.
Actual diameter versus nominal diameter
A true PAR36 sealed beam measures 114.3 mm. Many lamps sold as "4.5 inch PAR36" actually measure 111–112 mm, because they were designed for equipment brackets where a little clearance helps.
On a tractor this goes unnoticed. Inside a motorcycle bucket clamped by a fixed retaining ring, that 2–3 mm of slack is worked on by engine vibration every ride, and a loose lamp can eventually rotate or stress its wiring. A rubber trim gasket takes up the difference and damps vibration at the same time. Ask any seller for the real outside diameter in millimetres — a straight answer tells you a lot.
Which specifications actually matter?
Lumens, and which number you are being shown
Check whether a lumen figure is raw or effective. Raw output is what the bare LED chips produce on paper. Effective output is what leaves the lens after reflector and glass losses, and is typically 55–65% of raw. A lamp quoting 2,100 raw and 1,300 effective is being straight with you; one quoting only the larger number is not necessarily brighter.
Wattage — bigger is not better
A factory 881 halogen passing lamp bulb draws around 27W and produces roughly 800–900 lumens, converting most of its energy to heat. A well-built 18W LED delivers around 1,300 effective lumens on a third less current — 36W for a pair instead of 54W. That margin matters on older bikes with limited charging system headroom. Treat any 4.5 inch lamp advertising 60W or more with scepticism.
IP66 versus IP67
The practical difference is narrower than most listings imply:
- IP66 — dust tight, and protected against powerful water jets from any direction. Covers rain at highway speed, road spray and hosing down.
- IP67 — everything IP66 covers, plus short-term immersion.
A passing lamp is never submerged, so IP66 is sufficient for road use. What matters more is whether the rating covers the wire entry point as well as the housing. That gland is where cheap lamps let water in, and no IP number on a box confirms it was tested there.
Glass or polycarbonate lens
Polycarbonate is lighter and resists stone chips, but hazes and yellows under UV, so output drops over a few seasons. Glass stays optically clear for the life of the lamp, cleans without micro-scratching, and matches the sealed-beam look next to a chrome trim ring. For a lamp sitting behind a bezel that mostly sees rain, glass is usually the better trade.
Voltage range and polarity protection
A motorcycle charging system sits above 14V once running, with spikes beyond that. A driver rated for a wide DC input range — 10–30V is common — absorbs those swings without flickering at idle. Reverse-polarity protection matters on a circuit you are wiring by hand.
Vibration resistance
A V-twin at idle shakes harder than most vehicles at highway speed. Potted drivers and solid internal mounting are what keep an LED alive past the first season, and they are the most common reason a lamp that works fine on a truck fails on a motorcycle.
Colour temperature
6000K is a clean white that reads as bright, matches modern LED headlights, and makes road markings and signs stand out against the yellow cast of aging halogen. The trade-off is that cool white scatters more in heavy fog and falling snow than amber does.
How do you aim motorcycle auxiliary lights?
Aim auxiliary lamps 2–3 inches below their own centre height at 25 feet, angled slightly outward. LEDs put out far more light than the halogen they replace, so a lamp left pointing where the old one pointed will now reach into oncoming windshields.
- Park on level ground about 25 feet from a flat wall, bike upright, rider seated if possible.
- Mark the height of each lamp's centre on the wall with tape.
- Switch on the auxiliary lamps only, and aim the centre of each hot spot 2–3 inches below its tape mark.
- Angle each lamp a few degrees outward. This widens useful coverage without pushing light across the centre line.
Flood beams should be aimed lower still. A wide beam pointed level is the fastest way to get flashed by oncoming traffic, and it is why some riders wrongly conclude their new lights are simply "too bright."
Before you order: six checks
- Measure the lens diameter of your existing lamp. Nominal 4.5 inch is 114.3 mm — note the actual figure.
- Identify the connection: 881 bulb, H3 bulb, or sealed beam terminals. Photograph it.
- Measure usable depth inside the housing and compare against the lamp's stated height.
- Choose the beam pattern — spot for road riding.
- Choose the terminal type — screw terminals for a custom harness, pigtail for a sealed quick install.
- Confirm the lamp is intended for on-road use, and check auxiliary lighting rules where you ride.
Frequently asked questions
What size are Harley passing lights?
Harley-Davidson passing lamps are 4.5 inches (114.3 mm) in diameter, matching the PAR36 standard. They are fitted either side of the 7 inch main headlight on touring and Softail models.
Is PAR36 the same as 4.5 inch?
Dimensionally yes — PAR36 is defined as 4.5 inches. But "PAR36" traditionally implies a one-piece sealed beam with rear terminals, while many modern 4.5 inch motorcycle lamps take a separate bulb. Match the connection type, not just the size.
What bulb do Harley passing lamps use?
Later Harley touring models generally use an 881 bulb rated around 27W. Bikes from roughly the mid-2000s and earlier typically use an H3 bulb or a one-piece sealed beam. Check your own lamp rather than relying on the model name, since this changed across years.
Can I put LED lights in my factory passing lamp housings?
Usually yes, provided the LED unit is shallow enough for the trim ring to close and you have the right connector. Riders regularly fit LED sealed beams into original Harley and Indian buckets. Measure the internal depth first — that is what decides it.
Can I use a tractor or utility PAR36 LED on a motorcycle?
Mechanically it will usually bolt in, since the diameter is the same standard. The two things to check are beam pattern and validation: utility lamps are typically wide floods intended for low-speed work, and are not necessarily tested against the vibration a V-twin produces. A spot beam unit specified for motorcycle use addresses both.
How many lumens should motorcycle auxiliary lights have?
Around 1,000–1,500 effective lumens per lamp is a sensible range for a 4.5 inch auxiliary light. That comfortably exceeds the 800–900 lumens of a factory 881 halogen without producing more glare than the beam pattern can control. Beam shape matters more than raw lumen count.
Will LED passing lights trigger a bulb-out warning?
On most motorcycles, no — auxiliary lamps are usually not monitored the way headlights and turn signals are. If your model does monitor them, a load resistor added in parallel resolves it.
Are LED auxiliary lights road legal?
Rules vary by country and by state or province, and typically cover lamp colour, mounting height, how many lamps may be lit at once, and whether they must switch off with high beam. Check your local vehicle lighting regulations, and look for lamps that state compliance with a specific standard rather than a generic approval claim.
Do I need to re-aim after fitting LEDs?
Yes. LED output is brighter and more concentrated than the halogen it replaces, so aim both lamps against a wall before riding at night. Skipping this is the most common cause of complaints about auxiliary lights.
About this guide
Written by Handxen, a manufacturer of 4.5 inch PAR36 LED lamps in spot and flood beam configurations. The fitment and specification guidance here reflects production experience and installation feedback from riders. Where a figure varies by model year or by product, we have said so rather than generalising.
Harley-Davidson®, Road King®, Electra Glide®, Softail®, Indian Motorcycle®, Roadmaster®, Chieftain®, and all other model and manufacturer names are registered trademarks of their respective owners. Handxen is not affiliated with, endorsed by, or sponsored by any of these companies. Model names are used solely to indicate product compatibility. Always verify auxiliary lighting requirements in your jurisdiction before installation.