Towbar electrics?

[Crofty1984]

Hi all,
To add towbar electrics, can you just splice into the existing wires old-school style, or will that upset some clever electronic trickery?

[GraemeT]

Spliced in on mine (57 reg ) no problems using space behind cover on right hand side of the boot.

[Zen_Speedmaster]

I highly recommend using a bypass relay. You will still splice into the original van wires but you won't draw much power from them. The splice is only for switching the bypass relay which will then provide the voltage to the appropriate trailer light circuit. It's quite simple to do and you will avoid the risk of damaging the BSI.
There is a sticker on the rear lighting wiring in the van that warns that a drop of 10 or 100mA (can't remember which) will cause problems. A bypass relay is cheap and is not much extra work.