Story & Photos By Jim Clark (The Hot Rod MD)
Believe it or not, there are government regulations specifying how you must light your vehicle’s rear license plate. The regulations are part of Federal Motor Vehicle Safety Standard (FMVSS 108- Lamps, reflective devices, and associated equipment). Lighting the license plate is not actually a safety issue unless you consider identifying the bad guys as a safety concern. Most of us don’t pay much attention to this when building a hot rod but if you have ever watched “Cops” and heard the officer say, “I stopped you because your tag light is out” then you might wish that you had paid a little more attention to it.
If you are not changing the location of the license plate then the stock lighting should be sufficient to comply with the requirements. However, if you are building an early hot rod or custom then changes will probably be made to the location of the plate and lighting. The options are numerous and not all of them that are commonly used meet these requirements.
Following is the “legalese” language from the FMVSS 108 regulations as they pertain to license plate lighting.
FMVSS No. 108: License Plate Light Requirements
LICENSE PLATE LAMP (definition)
A lamp used to illuminate the license plate on the rear of a vehicle.
(12.7.4) MOUNTING LOCATION/HEIGHT
Each lamp, reflective device, and item of associated equipment must be securely mounted on a rigid part of the vehicle, other than glazing, that is not designed to be removed except for repair, within the mounting location and height limits listed in the below table, and in a location where it complies with all applicable photometric requirements, effective projected luminous lens area requirements, and visibility requirements with all obstructions considered.
· Vehicle type/size: Passenger Cars
· Mounting: On the rear to illuminate license plate from top or sides.
· Location / Height*: No Requirement.
*Height above road surface measured from center of device with vehicle at curb weight.
(12.7.15) INSTALLATION
As specified in FMVSS No. 108 paragraph S7.7.15, each license plate lamp installed on a vehicle other than a motorcycle or motor driven cycle must be of such size and design as to provide illumination on all parts of a 150 mm by 300 mm test plate. Each license plate lamp installed on a motorcycle or motor driven cycle must be of such size and design as to provide illumination on all parts of a 100 mm by 175 mm test plate. The light rays must reach all portions of an imaginary plate of the same size at least 25 mm. ahead of the actual plate measured perpendicular to the plane of the plate.
When a single lamp as shown in the following figure is used to illuminate the license plate, the lamp and license plate holder must bear such relation to each other that at no point on the plate must the incident light make an angle of less than 8° to the plane of the plate, this angle being measured from the edge of the light emitting surface of the lamp farthest from the surface of the plate.
MEASUREMENT OF INCIDENT LIGHT ANGLE
When two or more lamps are used to illuminate the license plate, the minimum 8° incident light angle must apply only to that portion of the plate which the particular lamp is designed to illuminate. The angle must be measured in the same manner as directed above.
The easiest way to provide a light to meet this requirement is by combining the license plate mount and the light on a separate bracket or one mounted onto a license plate frame. For many years the most popular light and bracket chosen was the one shown here on the rear of the McMullen roadster.
This light was usually mounted at the bottom of the plate because it stuck out too far at the top but as you can see from the regulations this does not comply with them.
This light and bracket is still one of the most popular and still available from a number of sources. The one shown is from The Hot Rod Company.
License Plate Bracket & Light
Chrome plated heavy gauge steel license plate 12-volt light with a stainless steel bracket. Fit standard US sized license plates. (HR-13556-A)
An alternative from The Hot Rod Company is this round LED light without a bracket that can mount to the plate or a license plate frame.
LED License Plate Light
LED license plate light is encased by a polished stainless steel housing. Clear lens with 6 white LED lights. Easy to hard wire with only two wires to connect. Designed with 8" between mounting bolts. (8-1/4" long x 3/4" wide).
Some early cars had a license plate light combined into the taillight housing like these stock ’32 Ford units from Speedway Motors. 1932 Ford Stainless Taillights
These are an exact duplicate of the original 1932 Ford glass lens taillights. Left light has a lens to illuminate license plate.
12 volt bulb
Highly polished stainless steel housing & rim
Cloth braided wire loom
Stainless steel screws
Glass red lens
3-7/8" diameter, 2-3/8" depth
2-11/16" overall depth (includes the wire retainer on the back of the lamp)
Frame & Light Installation
Recent offering from hot rod parts vendors make the lighting of the plate easier as there are many custom license plate frames with lights attached to choose from. The relocation of the plate on my roadster made it necessary to provide new mounting points and lighting. I was able to locate an aluminum frame with a small bar light attached to the top of the frame that didn’t stick out like a big lump when mounted legally at the top of the plate.
I bought this combination license plate frame with light from a vendor at the Portland Swap Meet but found it available from: Hot Rod Parts Clearance on eBay
Chromed Aluminum License Plate Frame With Light (Universal fit—50 State)
Mounting holes are countersunk for easy mounting.
Measurements are as follows: 12-3/8" X 6-1/2" X 3/8".
I chose to install threaded inserts into the rear panel below the decklid. They offer a permanent mounting point and eliminate the need for a ground wire for the license plate light.
You simply drill a hole and install the insert using a pair of wrenches and the special installation piece shown here.
An alternative to the threaded insert is these nylon inserts that usually fit into square holes on a bumper. They work fine but make a ground wire for the light necessary because they do not create a metal-to-metal contact with the car sheetmetal.
Mounting holes on the license plate frame are counter sunk so I chose stainless flathead bolts with allen-heads and placed rubber washers between the plate and inserts to space it off due to the curvature in the roadster panel. Grommets like these could be used as spacers or cut to adjust the spacing.
Lens is held into the bottom of the housing by two screws. Light mounts to the frame with two screws and the power wire exits through a hole in the housing and plate frame.
The unit I chose has a 12-volt bulb attached by this bracket inside the housing. There is also a version of this unit available with LEDs.
It was necessary to make a notch in the top of the license plate where the power wire was going to go through the rear panel. It will not show because the license plate frame covers the notch.
Masking tape was applied over the finished paint and a hole drilled for the power wire. If the plate and frame were not grounded then a ground wire would also need to go through this access point.
Grommets are available in a wide variety of sizes and for different thicknesses of panel. Choose one that fits the diameter of the wire or wires and has the appropriate gap for the panel.
A very small grommet was needed for the one power wire for the light. Using one that is too large could allow water or other contaminants to get in.
Wire is fed through the grommet and the license plate frame and plate installed with the four bolts. Counter sunk allen-bolts provide a smoother looking installation.
The wire is connected inside with some slack left so that the plate and frame can be pulled out in case the plate needs to be changed. Try to use a round connector on the power wire so that it might be able to be pulled through the hole for the grommet if the assembly had to be removed at a future date. Backside of the threaded insert can be seen in this shot of the rear panel.
After dark shot of the light shows that it illuminates the whole license plate, but not very evenly. A longer LED light or multiple lights would illuminate it more evenly.
This longer LED license plate light from United Pacific could be used without a frame or with the frame drilled to mount the light. You might be able to use it with the plain stainless steel frame shown here but the hole spacing on the plate doesn’t line up with the bolts on the light.
Frames With A Third Brake Light
License plate frames are also available with a third brake light or combination of third brake light and license plate light. They have to meet the regulations for a third brake light as stated in FMVSS 108.
FMVSS 108 Third Brake Light Requirements
MEASUREMENT OF INCIDENT LIGHT ANGLE
A high-mounted stop lamp mounted below the rear window must have no lens portion lower than 153 mm. [6 in.] below the lower edge of the rear glazing on convertibles, or 77 mm. [3 in.] on other passenger cars.
Height*: Not less than 34 inches except for passenger cars
* Height above road surface measured from center of device with vehicle at curb weight.
(12.9.5) ACTIVATION
Steady burning. Must only be activated upon application of the service brakes or by a device designed to retard the motion of the vehicle.
(12.9.10) SPACING TO OTHER LAMPS
No high-mounted stop lamp is permitted to be combined with any other lamp or reflective device, other than with a cargo lamp.
No high-mounted stop lamp is permitted to be combined optically with any cargo lamp.
These frames have a red light that might be employed as a third brake light if they can be mounted to fall within the height requirements and other parameters stated in FMVSS 108. If not they still could be used as an additional taillight but would still be illegal in the strictest interpretation of the regulations.
Summary
Like most other things automotive these days license plate and third brake lights are subject to a strict set of government regulations. The third brake light was added to the vehicle so that a driver would know when a vehicle was braking when following a vehicle close enough that seeing the regular brake lights was difficult. Generally enforcement is not very aggressive with either one, but not complying could leave a hot rod or custom car builder liable if involved in some unforeseen situation.
A third brake light is not required if the vehicle was not originally equipped with one but a license plate light was installed on some of the earliest models. There are a lot of choices available for meeting this requirement. Brackets with light or license plate frame with light are the ones most commonly used. Choose the one that looks the best on your vehicle.