Wizard Imports Limited

Towbar Relays


Wizard Imports Limited

TEB4 Fitting Instructions
How to fit unit
TEB4 Fitting instructions.pdf (31.72KB)
TEB4 Fitting Instructions
How to fit unit
TEB4 Fitting instructions.pdf (31.72KB)

TEB4           4 Way Bypass Relay     Fitting Instructions



This 4-way bypass relay may be used on negative earth vehicles that require a bypass relay to be fitted for circuit protection or to avoid confusing the bulb failure warning systems when towing a trailer or caravan.  Do not use this relay on circuits which have modulated* outputs to the rear lamp clusters, as relay chatter, or incorrect or non functioning of trailer bulbs may result.  Instead, fit the Universal 7 Way Bypass Relay TEB7AS.

Modulated outputs manifest themselves as low voltages, and often combine brake & tail or fog and tail lamps into one circuit.




Normal  rules of competency apply to anyone fitting this relay to a vehicle.

It should be fitted to negative earth vehicles only.     

Great care should be taken if the relay is fitted to a vehicle having multiplexed circuitry, and no attempt  should be made to interrupt or interfere with the BUS, the ESUs or the power cable of a multiplexed system. Power sources should be taken from the main fuse box or battery and signal sources from the regular 12v system directly feeding the various rear road lamps.



Route 28/0.3 cable (2.0 sq mm) from car battery to boot or fuse box, fitting an inline 15a blade type fuse holder, but removing  the fuse at this stage.


Offer up the relay to the above cable clusters and make  secure connections through the terminal blocks on the relay according to the below chart . 


Relay Terminal

Connection to Relay


28/0.3 (2.0 Sq mm) cable from car   battery or fuse box


Blue   Lead of 12N Cable


Brown   lead of 12N Cable


Red   Lead of 12N Cable


Black   Lead of 12N Cable


 Using scotch locks, solder joints or similar, attach the various leads coming from the underside of the relay to the car loom, teeing in at a point close to the car lamp circuit that is being sampled and avoiding any multiplex wiring or other devices.  If tail lamp cables are common to those for the brake or fog circuits in the car loom, or appear as low voltages, fit universal relay TEB7AS instead.


Signal Wire

Connection to Vehicle Loom


Fog Lamp


Off Side Tail Lamp


Brake Lamp


Near Side Tail Lamp


Secure firmly to vehicle chassis via   ring terminal

 Secure the relay to the harness or similar preferably using a tywrap.

Insert the inline fuse and test.  If a test board is used, it should have  21w bulbs on the flasher circuits as the buzzer only works under load conditions.

Note that the nomenclature and colour coding follows the format for the bypassing of the fog, tail and brake circuits on the 12N socket.  The 4 relay circuits are identical and can be used to switch any 4 functions.



Channel 1  blue cable switches output 2

Channel 2  brown cable switches output 5

Channel 3  red cable switches output 6

Channel 4  black switches output 7