I agonised over the same problem with the exact installation only 3 weeks ago.
Far easier than it looks! Other than access, which the majority needs to be done from the wheels arches.
Switchback bulbs plug straight into existing bulb holders.
The white wire just connects the two bulbs across the car. (If you unbolt the 10mm bolts across the front beam, the wire can be neatly hidden out of the way.)
The red wire from the switchbacks connects to the red wire on the controller.
Red and black battery leads are self explanatory.
As I said above, the red wire from the switchbacks connects to the red wire on the controller.
The black (earth) needs to be connected to any earthing point on the bodywork. There is an easy point 3/4 way back on the top of the o/s/f wing. The wiring can then be neatly clipped to the other cabling.
The yellow wire (dimmer) needs to be connected for MOT compliance. I founded the easiest way, was to pick up the purple wire on the underneath of the fuse box. Got the idea from here… https://youtu.be/X41dfRI1w3o
Very happy with the result
Any other questions, just shout.