right so are you putting one under the bumper or are you going to as i have done with many incorperate it as one of the reverse lights o/s one obviously
all you have to do is find the wire that goes live with the fog switch and swap it with the relavent reverse light wire then put a red led bulb in the reverse light .
Sorted it thanks to a mate and his multimeter. The foglight live is with the driver side reverse light. so just it looks like the previous owner changed the wiring loom with the lights, and got rid of the rear fog part as the lexus lights were for a car with a bumper mounted fog, so not needing the extra bulb.
So i've swapped the wiring round and fitted a LED red bulb in the drivers side reverse light, so one side is reverse, one side fog.