Stunning 240 estate

[Laird Scooby]

Originally Posted by john.wigley

That is not a bad idea at all, 'L.S.'. The 2 series is well up to occasional light towing duties and as you say many - especially estates - were so equipped from new. If Alan can bear to fit one to the R.B. it may be the answer to his dilemma.

I towed a light 6' x 4' trailer extensively in period with both 2 and 7 series cars with few issues. My cars were equipped for towing when I bought them and the BFWL functioned as normal, so presumably wiring for same was standard in period. I don't know if it will be of any help to Alan, but I also successfully carried one of those light 'spectacle' bike carriers directly on the towbar. They were ideal for mopeds and lightweight motor cycles, but I doubt that they would be suitable for heavy machines like Alan's Triumph.

Regards, John.

The other thing is John, i speculated on the other Volvo Alan may be bringing to the mix further up, if it's my first suggestion (262C) or the last one which i'm keeping quiet about for now, either of those would be well up to towing but again, if auto would need an auxiliary ATF cooler to tow more than 1000kg.

The way the BFU works is it passes the current to a pair of bulbs in the circuit through a pair of coils, each wound in opposite directions next to a reed switch. If both bulbs are working, the fact that each coil is wound in opposite directions to the other means they both produce a magnetic field in the opposite direction - a North pole and a South pole of a pair of bar magnets if you will. These cancel each other out so the reed switch doesn't move.
However if one bulb is blown (or there is a bit of resistance in the circuit like a bad earth or even a different make bulb) then there is only one magnetic field which operates the reed switch or in the case of resistance, a smaller magnetic field. The larger overcomes the smaller and operates the switch. Note that if both bulbs or the fuse for that circuit fails, no warning will be given.

With this in mind, you can imagine the wires carrying the current have a finite capacity of current. As such adding extra bulbs in the form of a trailer board/trailer lighting "downstream" of the BFU will overload the wires and burn them out resulting in that circuit being inoperative. Therefore the towbar wiring must be connected "upstream" of the BFU, i.e. before the power to the various monitored circuits passes through it.
Obviously this means the trailer lighting isn't monitored.

Meanwhile i'm waiting to see what Alan buys (assuming he does) to know if that woulod be more suitable as a towcar.