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Towbar, Trailer & Bike Rack Electrics

If you have a trailer or rear mounted bike rack and it obscures the vehicles rear lights and license plate, then you will need a light board, or you could be breaking the law?

What can I do?

You can either get some extra lights fitted by a garage or towbar specialist, or you can fit a socket or connector to the vehicle yourself…

Trailer or Bike Rack Electrical Connector Socket
Trailer or Bike Rack Electrical Connector Socket

How to Fit a Trailer or Bike Rack Power Socket:

The section below ‘Quick Overview‘ is a short summary of what’s required to fit a trailer or bike rack connector.

…and contains the following sections:

More detailed descriptions can be found in the following articles:

Trailer & Bike Rack – Type of Electrical Connectors

Trailer Socket 12N 13 Pin (ISO 11446)
Trailer Connector Differences:A Brief Summary of the type of Trailer Connectors (by region):Socket Types: Trailer and Bike Rack connectors can come in a variety of shapes and sizes depending on […]

Trailer & Bike Rack – The Bypass Relay

Vehicle Trailer & Bike Rack – The Bypass Relay
What is a Bypass Relay:How does the Bypass Relay Work:Which Bypass Relay Should I buy:Hints & Tips: What is a Bypass Relay? Since about 1990, most cars have been controlled […]

Quick Overview

Parts Required:

What parts are needed:

Note: Dependant on what you buy, sometimes wire is supplied with the product.

The Trailer Socket:

A trailer socket usually conforms to a specification, dependant on which part of the world you live in. The most important thing is to check what’s fitted to the trailer, or bike rack you intend to use (see)…

The Trailer Socket Mounting Bracket:

Normally a pressed steel bracket shaped to take the trailer socket, with all the mounting holes pre-drilled. This usually bolts to the towbar. If a towbar isn’t fitted, then an additional bracket may be required.

A mounting bracket with an open slot is preferable, as this allows the trailer socket to be removed from the bracket without disconnecting the wiring.

The Bypass Relay (The Interface to the Vehicle Electronics):

The bypass relay (The interface to the vehicle’s electronics) acts as an isolator between the tow bar electrics and the vehicle’s electronics. The bypass relay is actually one or more relays. Typically, a bypass relay is described by the number of ‘way’s’ it has. I.e. 1 way, 2 way, 4 way, 7 way, etc.

No. of Ways It controls the…
1 way A single light, or set of lights.
7 Way Rear lights (pair).
Rear brake lights (pair).
Rear left indicator (single).
Rear right indicator (single).
Reversing light(s).
Fog light(s).
Number plate light(s).

Vehicle Wire (Cable):

The size and type of cable is important…
  • If the wire is too small it will overheat and could catch fire.
  • The cable needs to be of the correct type (flexible and resistant to low and high temperatures). Otherwise, it could break, or cause electrical issues.
You can:
  • Check the vehicle specifications, or see what’s already fitted to the vehicle?
  • Installation instructions should specify the size of cable required (for electrical components).
  • Or purchase components that have the cable included.

Note: Wire can be purchased as a single trailer light board cable with all the individual colour coded cables within, which may make life easier.


The Links Below Take you to More Detailed Descriptions on Towbar, Trailer & Bike Rack Electrics :