I started researching some laws regarding lights and discovered much insanity. That does not surprise me given California and the attitude of "there is no problem more laws cannot solve" which ends up creating some stupid laws beyond the intent.
While many of these things are not enforced on motorcycles, they could be. Most states have thousands of vehicle codes basically allowing an officer to pull anyone over at any time for any reason, fortunately that does not happen as often as it could. CHP is increasing motorcycle checkpoints, the NHTSA is trying to make a program national to do motorcycle only checkpoints for equipment violations (and some other motorcycle related things).
Disclaimer I am not a lawyer, this is not legal advice. In addition to State laws there are also city and county laws which may prohibit additional things. These laws can change at any moment yet this post will not be edited in the future, you are encouraged to validate everything here on your own. I have probably missed a whole bunch of laws as well. When in doubt dont do it until you have consulted a lawyer and/or are willing to risk getting a ticket.
I have not observed enforcement of many of these things. Brighter than stock headlamps I see all the time. Tinted motorcycle windscreens I also see. I have observed blue headlamps with no citation forthcoming. I have seen many many motorcycles with the license plate tucked so far under the bike its barely visible at all (dont have the statute but I am sure that is not legal cause the photo systems cant see it). On the flip side I have seen people posting about getting a ticket for under body lights on their car (despite a statute specifically allowing them). When it comes to motorcycles I think the general rule is 'if it increases safety without being distracting and impairing other drivers then its fine'. If you are racing, exhibiting excessive speed, doing stunts, etc then all rules are off and they will probably look for everything they can possibly get you on.
Fender Eliminator Kits
Lack of white rear license plate light (24601 VC)
Rear Reflectors
Headlamp upgrades
It is legal to have a headlamp modulator providing (25251.2 VC)
During darkness (25651 VC)
Exhaust
Must comply with smog rules (27156 VC). See Air Resources Board web site for more info and list of parts that are legal.
New law that takes effect for bikes model year 2013 you will not be able to modify to be louder than stock exhaust
Bling/Misc
All lights must be specifically required by statute or permitted by statute, undefined lights are illegal (24003 VC).
All flashing decorative lights are illegal (25250 VC).
Lights attached to tire valves are illegal (24003, 25250 VC).
Lighted license plate frames are illegal (unless red) (24003 VC).
It is illegal to have illegal lights on a vehicle whether or not they are operating (24003 VC).
it is apparently legal to have underbody lights (25400 & 25401 VC)
Windscreen
Cant tint your windscreen. They define "motor vehicle" to include motorcycles. (26708 VC)
Sources (and probably a few I forgot to paste in here)
CHP - Asia Pacific Islander Outreach
http://www.chp.ca.gov/publications/pdf/chp888.pdf
V C Section 25400 Lighting Requirements
V C Section 25401 Diffused Lights Resembling Signs
V C Section 24003 Vehicle With Unlawful Lamps
V C Section 25250 Flashing Lights
V C Section 26708 Material Obstructing or Reducing Driver x2019 s View
V C Section 25251.2 Motorcycles Headlamp Flasher
While many of these things are not enforced on motorcycles, they could be. Most states have thousands of vehicle codes basically allowing an officer to pull anyone over at any time for any reason, fortunately that does not happen as often as it could. CHP is increasing motorcycle checkpoints, the NHTSA is trying to make a program national to do motorcycle only checkpoints for equipment violations (and some other motorcycle related things).
Disclaimer I am not a lawyer, this is not legal advice. In addition to State laws there are also city and county laws which may prohibit additional things. These laws can change at any moment yet this post will not be edited in the future, you are encouraged to validate everything here on your own. I have probably missed a whole bunch of laws as well. When in doubt dont do it until you have consulted a lawyer and/or are willing to risk getting a ticket.
I have not observed enforcement of many of these things. Brighter than stock headlamps I see all the time. Tinted motorcycle windscreens I also see. I have observed blue headlamps with no citation forthcoming. I have seen many many motorcycles with the license plate tucked so far under the bike its barely visible at all (dont have the statute but I am sure that is not legal cause the photo systems cant see it). On the flip side I have seen people posting about getting a ticket for under body lights on their car (despite a statute specifically allowing them). When it comes to motorcycles I think the general rule is 'if it increases safety without being distracting and impairing other drivers then its fine'. If you are racing, exhibiting excessive speed, doing stunts, etc then all rules are off and they will probably look for everything they can possibly get you on.
Fender Eliminator Kits
Lack of white rear license plate light (24601 VC)
Rear Reflectors
Headlamp upgrades
It is legal to have a headlamp modulator providing (25251.2 VC)
- it alternates between high beam and low beam
- it modulates between 200 and 280 flashes per minute
- it does not modulate at night
During darkness (25651 VC)
- reveal a person at 100 feet when operated at any speed less than 25 mph
- reveal a person at 200 feet when operated 25-35 mph
- reveal a person at 300 feet when operated at a speed greater than 35 mph
- if high/low capable the above applies to high and low must reveal a person 100 feet ahead
- if single beam, when motorcycle is loaded at 25 feet head the light has to be projected lower than level of the center of the lamp
Exhaust
Must comply with smog rules (27156 VC). See Air Resources Board web site for more info and list of parts that are legal.
New law that takes effect for bikes model year 2013 you will not be able to modify to be louder than stock exhaust
Bling/Misc
All lights must be specifically required by statute or permitted by statute, undefined lights are illegal (24003 VC).
All flashing decorative lights are illegal (25250 VC).
Lights attached to tire valves are illegal (24003, 25250 VC).
Lighted license plate frames are illegal (unless red) (24003 VC).
It is illegal to have illegal lights on a vehicle whether or not they are operating (24003 VC).
it is apparently legal to have underbody lights (25400 & 25401 VC)
- Must be less than 0.05 candela per square inch of area
- must be diffused nonglaring light (no visible bulb at all)
- must not flash or blink
- must not resemble any official traffic control device
- must not display red to the front but may display other colors
- must not resemble any required lamp, reflector, or other device
- must not be installed within 12 inches of any required lamp or reflector
- must not be installed in a place that would interfere with the visibility or effectiveness of any required lamp or reflector
Windscreen
Cant tint your windscreen. They define "motor vehicle" to include motorcycles. (26708 VC)
Sources (and probably a few I forgot to paste in here)
CHP - Asia Pacific Islander Outreach
http://www.chp.ca.gov/publications/pdf/chp888.pdf
V C Section 25400 Lighting Requirements
V C Section 25401 Diffused Lights Resembling Signs
V C Section 24003 Vehicle With Unlawful Lamps
V C Section 25250 Flashing Lights
V C Section 26708 Material Obstructing or Reducing Driver x2019 s View
V C Section 25251.2 Motorcycles Headlamp Flasher