How front and rear lights are wired to the bike

A wired light is a lamp with a cable that ends at a port on the bike. Where that port is, and how the cable gets there, depends on the bike. This page gives the general picture. Your manual gives the real one.

Where the power comes from

A general reference on bicycle lighting separately notes that for higher-powered lights, an external battery pack of 12V VRLA battery is often required¹. That is a different setup from the bike-wired lights below.

One maker describes two types of connection on its bikes. On its full-power systems, the lights go straight into ports on the motor². On its lighter systems, lights connect through a splitter at the display, rated at 12 V only, 8 W/650 mA max.²

The maker is firm that the two aren't interchangeable: the splitter cable must not be used with full-power systems². A part that fits one bike can be wrong for the next.

The cable run

Cables go from the port to the front light and, if there is one, to the rear light. The rear run needs particular care, as the next paragraph shows.

The maker's guide admits a rear light often can't be fitted at all, or takes more labour². It gives an example of a blocker: a dropper post does not allow routing through the seat post². Some frames also need a different cable entry port, since the original may not fit the extra light cable².

Connectors and covering

The guide lists small parts a fitting may need, including shrink tube to cover any bare wiring and connectors². That's the maker's own list for its own bikes, written for retailers. It isn't a how-to for owners.

The guide covers a bike that powers off. For a wrongly rated light, it says to disconnect the light immediately². If it happens with an approved rated light, it says to re-check the cabling to ensure all connections are covered correctly and no short-circuiting occurred². In both cases, treat it as a reason to stop and ask a shop or follow your own manual, not as a repair recipe.

For that reason the maker wants its retailers to do the fitting for riders².

What to ask before you buy a wired light

• Does my manual show a light port, and where is it?
• What is the port's output rating, in the maker's words?
• Is the connector on the light made for that port?
• Will the cable fit my frame, or does it need a new entry point?
• Can a rear light be wired at all on my bike?
• Who will fit it, and does the maker want a shop to do it?

If the answers aren't in the manual, ask the maker. Don't cut, splice or guess at a connector. A clip-on light avoids all of this, as the integrated versus clip-on page explains.