Have a time away from this to clear your head, the smoke has escaped from the proper wires, but it can be replaced (even on Lucas equipment). Make sure battery cables and earth connections are clean and properly snugged. Double check the harness in that there are no signs of damage from improper routing that caused pinching, cuts, chaffing, over stretched/binding, bad splices, etc. Be critical in your assessment as it doesn't take much to cause a failure. I once had a zip tie hold the harness too tight near the head stock and this caused one of the pins in a connector to separate as it wasn't fully seated internally. Bars to the left, lights on and we have ignition, to the right it was no start and no lights, but if done after starting it would keep running. Love the Italians, it affected the start circuit only and wiggling the wires duplicated it like it was an internal stretch and failure, but it wasn't. Finally after checking 1 or maybe 100 more times ::) I noticed the unseated pin amongst the others and it would simply move in or out from contact as the bars moved the harness. A fully seated pin and/or a little more slack would likely have kept her working fine. BMW also had "stretching" failures from harnesses being installed too tight in the headstock area, so keep an open mind as to what "looks good" may have succumbed to a minor, yet still critical failure.
Regardless (for the moment) 15 or 5 amp being spec'd, the systems were fine and working previous to this failure (correct?) with whatever fuses were installed, so something new, be it moisture, chaffed insulation or a bad connection, etc., came into play on this ride.
Not being there it is hard to see your situation nor observe your protocols and abilities in trouble shooting so please don't be offended in my points or questions.
You pulled apart the connections and sprayed them with cleaner. Did you remove them all from the circuit and did she still pop a fuse with everything "off line"? If she passed this test, did you then systematically reconnect one at a time checking the new fuse as you went along? At the magic point of connectivity the culprit would/should overload the fuse and that would have been a huge tell on where to make the repair.
If you did something similar to the above and all the components "passed" the simple R+R test and the way you describe the "new" failures taking other circuits fuses out leads me to think it has to be a dead short in the wiring itself. Did you use a multimeter or other means to check continuity when the connection plugs were apart? Do not assume anything and make doubly sure any added crimp or other type spliced connections are proper and insulated (soldering is best).
Trying to ask clearly, but if not, hopefully the gist of what I'm describing makes sense to you. Finding electric faults is not hard per se, but it can be hard on you. Keep it simple and methodical and you'll have it. Maybe a knowledgeable mate with a fresh set of eyes can give you a hand and double check some stuff with you, even just an extra pair of hands during testing can make a quicker and less frustrating job of it.
Good luck
