Having asked a question recently about DRLs I am fitting to my MX5 I have decided on the following:
I will take an ignition controlled live (which I will fuse) from the fuse box to power the DRLs so that they come on when the ignition is turned on. I want them to go off completely when the headlights are turned on so intend taking a feed from the headlight wiring. To do this I have been advised to use a 5 blade change over relay which I have. Question is how do I wire it? Can anyone advise what goes to which numbered blade on the relay please making it understandable for an electrical numpty ie; me! Thanks in anticipation.

Pin 30 is your power supply.
87a to the drl +ve
86 from sidelight supply (goes live when sidelights on)
85 earth
87 should be insulated/unused (but will go live when sidelights on)

Others may do it differently? The relay is merely to switch the DRLs off when the sidelights go on.

what is the wiring loom based on?
do you already have a relay for the sidelights?

one note, a relay is simply: an electrically actuated switch.