This particular task is something that any motorcycle mechanic should be able to do. The guy I consider to be my independent mechanic is the Kawasaki dealer a town over, but the bulk of his business is actually used bikes. It's the kind of place that I could go and run this idea past the mechanic over a cup of coffee and he'd either point out the possible pitfalls, give me a few tips, or say "You better bring it in" only if that's his honest assessment.
I forget which city you are in right now, but Yelp has lists of motorcycle repair shops in
San Antonio and
Austin.
It seems that your bike has had enough problems for long time and none of the mechanics you have taken it to has made any lasting improvement. They are nickel and diming you to death. That has gotten you to the point that the bike is pretty much a paper weight right now. The best option, and long term best value, really may be to take it to the Harley dealer to at least diagnose the problems.
I called
Cowboy's Alamo City Harley-Davidson in San Antonio and they do pre-buy inspections for something like $57 plus tax. It's basically the same thing they do to evaluate trade in bikes and pretty much what you would be asking them to do. Just be up front that it's a bike you already have and need some guidance. They just need to spend 0.5-1.0 hours of diagnostic time and come up with a plan on how to get the bike roadworthy again. They could read that code causing your check engine light and provide a punch list of work that needs done. I'm not saying to have them do any or all the work, but they would at least give you some guidance of what needs done and what it would cost.
There are other Harley-Davidson dealerships in
San Antonio and
Austin. Their prices for pre-buy inspections will vary. For example, I also called
Loess Hills Harley-Davidson here in Iowa and they do a similar inspection and charge for an hour of diagnostic time, which is around $120.
In past threads you have said that it's been showing a check engine light for a long time. Those are prompted by a diagnostic code, which somebody should be able to read. That's why diagnostic codes exist. If the mechanic doesn't know what code is causing the check engine light he's just guessing. As I recall, your independent mechanics last guess was that you need to spend better than $1,000 for to replace the complete wiring harness. If he's wrong, you will have spent that money for nothing and missed the opportunity to do what really needs done to make the bike rideable again.