Bypass Relay Checklist

The following checks will tell you which bypass relays to use.

  1. Check the vehicle's handbook and check CarData on this web site to see which type of bypass relay the vehicle requires.
  2. If you think the vehicle may not require a bypass relay, check the fuses AND wire sizes in the vehicle loom to see whether additional current can safely be carried to supply the trailer road lamps directly. (Determine wire capacities by counting the strands, not by looking at the apparent wire thickness. Thinwall cables may look thinner but have higher capacities than previous "conventional" cables. (See cable chart.) If you are in any doubt, you are probably wise to fit a bypass relay.

Once you have identified which circuits need bypass relays, use the checklist below.

Reversing Lamps: Capacity built into the seven way relays

Vehicle Circuit Relay
Stop or fog lights, etc. (Single) TF1011
Tail lights only (Double) TF1013
Flashers only (Bypass Relay) TF110R
Stop lamps and Tail lamps (3 lamp) TF1013
SmartCAN multi-compatible CANbus module TF2302
All lamps (Universal Smart LOGIC Bypass) TF2218/7E
If you decide to cut out the vehicle's foglamp when towing, use TFC2


Fog cut-out (Twin) TFC2