It's pretty easy in the long run. It relies on the fact that the coil in the relay isn't polarity-specific, so you can have it work no matter which way you hook up the wires to pins 85 and 86.
If you want to be able to use high beam without the driving lights on, then hook up a relay in the normal fashion in either of the lines going to pins 85 or 86 in the picture below. No power = no activation = no driving lights. Like this: earth in cabin to a switch, then the output of that switch to pin 85 of relay in the engine bay. Pin 86 of this new relay to positive. Pin 30 should come FROM the headlight (let's say the light blue line) and pin 87 of the new relay should go to pin 85 of the other relay.
Thanks Tony, much appreciated, will give it a go.
