Multi Function TAIL LIGHTS








TLC #231-1   FMVSS #108* “CLEARANCE” and “OPTICAL COMBINATION” Clarifications

July 16, 2008

To:        Trailer, RV, and Truck Manufacturers
From:    Dennis G. Moore, President

I’ve recently sent the attached writing to both NATM* and NMMA** Legal Departments as I have reason to believe their “Certifying Inspectors” have been misleading Trailer and RV Manufacturers as to the “Interpretation” sections of Federal Motor Vehicle Safety Standard #108 (FMVSS #108) that regulate mandated Clearance Light Positioning and Visibility Scopes.                 

*National Association of Trailer Manufacturers
**National Marine Manufacturers Association

Also, the subject of Optical Combinations seem to be a subject “not clear” to NMMA and NATM Certifying Inspectors nor to most Trailer and RV Manufacturers as well. I know both these subjects suffer from long term misunderstandings and confusion, and I also know that NHTSA makes no attempt to clarify these subjects … so confusion and mandate violations continue, spurred on with a “let it rip” NHTSA attitude that’s resulting in Trailer, RV, and Truck Manufacturers … as well as Aftermarket Replacement Distributors … being led into decreasing the safety of their vehicles while increasing their public liability exposureAll this chaos while NHTSA employees remain oblivious and immune to any liability using their usual “hide behind” and “back and fill” excuses.

In any case … I’ve tried to clarify the “Clearance” Light and “Optical Combination” subjects with the attached writings. 
If read carefully while comparing each confusing detail to the latest FMVSS #108 printing on … and asking NHTSA’s Legal Counsel division for “Legal Interpretations* “ when needed … can eventually result in a full understanding of the actual Intent of the 1966 Vehicle Safety Act and … hopefully help to clarify the resultant FMVSS #108 Mandates.               


We hope you take this opportunity to try and learn about these subjects in detail so you can make safer vehicles at less cost and perhaps better appreciate our quality, safety features, and overall value when compared to cheapened Chinese Copies and (twice the $ cost) Multi-Function LEDs that are beginning to generate leaking and failure “returns” that are turning happy profit situations into $ loss and grief ridden situations.

Home of DRY LAUNCH® and CONVOY® Quality Vehicle Lighting Products

July 16, 2008

*Federal Motor Vehicle Safety Standard #108

Dennis G. Moore, Sierra
Design Manufacturing, Inc.(Formerly Sierra Products, Inc.) Livermore & Sonora, CA

Everyone answerable to Trailer, RV and Truck Federal Lighting Laws should consider the following:


1. Clearance Lights must be mounted“as close as practical” to “represent the extreme width”* of the Vehicle.  Contrary to popular

beliefs … there is no Federal “Legal Interpretations” on record that Carte Blanc allows up to 6” mountings of Clearance Lights inboard of the Extreme Width.  Study the three attached NHTSA Legal Interpretations and also consider checking our other writings on this subject on our website.

*The term “Extreme Width” is used interchangeably with “Overall Width” by D.O.T. and NHTSA The 6” inboard mounting discussed in the attached NHTSA “Interpretations” still is required to comply to the “as close as practical to represent the extreme width mandate”.  These Interpretations verifies the fact that mounting Clearance Lights “not” at the extreme width is only acceptable if there’s absolutely no “practical” way to better represent the “extreme width”It goes without saying … what is “practical” represents a subject no Defendant or Lawyer would want to have to define to a Jury in a Liability Court Case.

2.       Only one Rearward Pointing Red, Clearance Light is required by FMVSS #108 on each side of Trailers, RVs and Trucks that are over 80” in width.

3.       NHTSA allows Clearance Lights to be mounted from 12 inches to 10+ feet above the pavement.  However, when mounted more than ≈40” above the pavement, Clearance Lights losesome … most … or all … of their safety effectivenessWho cares? knowing how wide a Trailer, RV or Truck is up high … beyond traffic eye level?  Common sense tells us that we should be warned of “Extreme Width” at close to traffic eye level so we are made aware of what we mustclear” in a closing fast, evasive scenario at night … or in a torrential downpour, or blizzard, or under any other limited visibility condition.

4.       FMVSS #108 mandates that Clearance Lights must be clearly visible from 0° to 45° “Outboard”*; however, be also aware that NHTSA used to mandate a 0° to 45° “Inboard”* visible scope as well, which they rescinded several years ago for illogical and downright “stupid” reasoning**.  Here’s another regrettable example of the defiance of common sense sanctioned by NHTSA and SAE.  *and within 10° Up to 10° Down **See our additional Website writings on this issue

5.       Also, be aware that Clearance Lights … as well as all other Side and Corner mounted Lights … are allowed by Federal Law to “stick out” beyond the Standard 102 inch Trailer, RV and Truck width limit, as are the Mirrors. In real life applications … if a typical Trailer, RV or Truck Multi Function Tail Light Assembly is mounted to adequately represent the “extreme width” … in effect … it actually seconds as an “extreme width” Clearance Light.  However, even under this circumstance, FMVSS #108 still mandates that an extra small bulb or LED Cluster must be used  independent of the Multi Function Light Tail Light Assembly while “also” representing the extreme width … thus providing … in effect … a redundant Clearance Light. Obviously, adding a pair of superfluous Bulbs or LED Clusters on millions of Trailers, RVs and Trucks … that are really not needed forces a more expensive and more energy-consuming situation onto the American Public.  Nevertheless, this is what the powers to be at NHTSA and SAE have mandated, even if the Tail Light Assembly represents the“extreme width”.  Here’s still another example of NHTSA’s and SAE’s defiance of common sense.

In actual use in traffic, as long as an “extreme width” mounted Tail Light keeps working, the width is properly represented, and the fact there is no Back Up Clearance Light, represents an Inconsequential to Public Safety”* situation because the “extreme width” would always be adequately represented as mandated by FMVSS #108.       *This is an official “legal” allowance provided by FMVSS #108

6.       When a Trailer, RV or Truck … over 80” in width … uses Multi Function Tail Light Assemblies that are “not” mounted to represent the “extreme width” then, “Independent” Clearance Lights must be used in order to satisfy the FMVSS #108 “extreme width” representing mandate. In this kind of an independent Clearance Light scenario, the 8th Function Clearance Bulb addition would not be required! Contrary to popular belief… Over 80” and Under 80” FMVSS #108 Classifications refer only to the 11-5/8in² and 7-3/4in² “Effective Projected Luminous Lens Areas”* mandated by FMVSS #108, whereas, over 80” and under 80” does “not” refer to Multi Function Lights that have … or do not have … a separate 8th Function Clearance Bulb.        
* See our Website for further discussions on “EPLLA” This “8th Function” versus “EPLLA” misunderstanding is widespread and must be clarified to all involved!

7.       Again! … mounting a Red, rear pointing “extreme width” indicating Clearance Light completely independent of the Multi-Function Tail Light Assembly is all that’s needed to save the … 8th Function … Bulb and Power expense – only one pair – not two pair – are required. Also, realize that in addition to the rear pointing Red Clearance Lights, a pair of front pointing Amber Clearance Lights are also mandated to warn oncoming traffic of extreme width, meaning that Four … 2 Red and 2 Amber … Clearance Lights are needed in all. A more economical scenario to the using of Four independent Clearance Lights, is to consider our dual-colored (Red/Amber) outboard fender-mounted WingTips®, which saves the expense of two Front pointing Amber Clearance Lights, not to mention providing more conspicuous, and nearer to eye level, Side (pointing) Marker Lights plus giving the Driver a valuable, rear view mirror seeable … and nearer to traffic eye level … “Back Up, Location Indicator” that all Big Rig drivers wouldn’t be without.

Using this economical approach provides Trailer, RV and Truck Manufacturers (and ultimately the vehicle owner/driver) saved dollars $ and provides bonus safety features by using just two of our Wing Tips® that require the use of only a single 1/3 Amp, easily found bulb, and an always serviceable “Rustproof” Bulb Contact System.  *Instead of Four Independents This not only reduces the expense of Four Clearance Lights to Two, but it also provides drivers with Safety plus Peace-of-Mind features none of our competitors offer.   

Compare the total cost of using a pair of any of our 7 Function Light Assemblies complimented with a pair of our Red/Amber, 5 Function Wing Tips® to the total cost of using any of our competitor’s 7 Function Light Assemblies complimented with four separated conventional Clearance Lights.  You’ll find WingTips® save everyone involved money and complications!


1.  As I pointed out earlier … FMVSS #108 does “not” allow a Clearance Light to be “Optically Combined” with a Tail Light.  This means that both the Clearance and the Tail Light Functions must depend on “separate” Illumination sources.  However … contrary to popular beliefs … both Functions are allowed to share common or overlapping Lens Areas as long as both Functions are able to pass independent Photometric FMVSS #108 mandated tests on their own with the other extinguished.       

2.   Also be aware that FMVSS #108 “does allow” the rear Side (pointing) Marker* light’s illumination source to be “Optically Combined” ( shared) in order to also illuminate the Tail Light Test Pattern Scan as long as both functions can independently and simultaneously pass their corresponding FMVSS #108 Photometric Scan requirements.  This means both functions are allowed to use a single, illumination source while also being allowed to share common and overlapping lens Areas.  
*which I prefer to call a “Traffic and Pedestrian Intersection Light

3.  Also, know that a rear or front pointing Clearance Light is allowed to be “Optically Combined” with a rear or front Side (pointing) Marker Light.  Taking advantage of this legal Clearance/Side Marker “Optical Combination” allowance has saved knowledgeable Trailer, RV and Truck Manufacturers a lot of dollars over the years because only a single Illumination source and a contiguous lens for both the Clearance and Side Marker Functions are permitted by FMVSS #108, thus eliminating the $ expense $ of two lights as well as the corresponding $ installation, $ wiring and $ power consumption costs.Usually you’ll see this Combination used on corners of full width Big Rigs, Trailers and RVs that don’t use fenders, whereas a small light with a non shadowed* FMVSS #108 180° Compliant output is mounted at a 45° Angle so that the 0° to 45° Outboard Visual Path satisfies compliancy for the Clearance Function while also projecting adequate Side (pointing) Lighting to warn Intersection Traffic and nearby Pedestrians of the vehicle’s existence, width and length.   
*The bulb can’t be shadowed by the bulb or LED holding system In summary … be aware that most of the knowledge and facts outlined, above, can be verified and studied in more detail on our other Web writings under, or … by gambling a lot of your time and patience.  You can confirm my statements using NHTSA’s Website at, which you’ll find represents a confusing and lengthy challenge, but nevertheless, represents current law.

Also, know that anyone trying to tackle any confusing FMVSS #108 Subjects* is supposed to be able to receive “timely” clarifying explanations using NHTSA’s “Legal Interpretation System”, which (I’ve been told) must result in a NHTSA “Legal Counsel” answer in no more than 6 weeks.  Try out this Taxpayer paid-for NHTSA service and … see what happens!              *And there are many      

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