"I'm blown away by the number of relays in this electrical system!"

The best quote from the above link.

Finding a short like this is tedius and very time consuming. In an industry where the equipment is mission critical and the equipment can not be replaced, it must be repaired, funds are available to diagnose and fix the problem.

In the consumer market, no one is willing to pay for this type of work, so you will not find a skilled and experienced mechanic at a dealership or private garage that does this type of work.

I have worked on electrical systems where a component that would fit in a small tacklebox costs more than $50,000, when a problem on one of those system cropped up, we fixed it, no need to ask the owner first.

I have also worked in both private garages and dealerships on cars and trucks. I would never even pop the hood on a problem like yours without a complete wiring diagram in my lap (not on a danged computer screen), and a deposit (as in downpayment) from the customer for 20 hours labor to just start work on it. It would be only done on a time and materials basis, using a timeclock to punch on and off the job. I expect to get paid for all my time on the job, no matter if a fix is ever found or not.

Hardly any car owner would agree to these terms, but I have bills to pay just like everyone else, and this is how I earn my pay.

IMHO this sums up the "why" no one can fix it.

You will have more luck fixing it yourself, using mechanic forums as mentioned above. My experience with Ford elect systems leads me to believe that once you start having problems, get ready for more and start carrying a fire extinguisher.