Thanks for your reply. Here's a picture of the connectors in place with the airbox lid removed (the green connector is still joining two wires):
tn_IMG_0832.JPG
It's a bit tricky to photograph with the airbox lid attached, but here it is from the right side:
tn_IMG_0804.JPG
...and from the left side:
tn_IMG_0807.JPG
All four wires run straight across the front of the airbox then through the front of the frame. From looking at some other posts I wonder if whoever bodged the fix previously re-routed the wires so they're now in the wrong place. Should the ignition wires run from the loom backwards under the frame rail just in front of the throttle bodies then around that rail? Seems like a bit of a convoluted path but it would avoid being right under the intake I suppose.