Mark,
What I say is open to a correction later, but I already had an unswitched fused live
direct from the 'battery' area to power the additional headlight relays. That was used
in conjunction with switched live, I think, from the ign at the coil.
Just visible in the 2nd pic is the heavy red cable which goes to the two, just visible,
lamp relays. I'd purchased the wrong inertia switch (N/O versus N/C), hence the relay next to it!
N.