I'm sorry you are having problems with Harley. Please don't give up!
Suggestions for success: Do your absolute best to keep a regular schedule of outings for Harley. When he does his business correctly outside, praise him profusely -- never stop giving praise no matter how old he gets. Maybe include a small treat for awhile.
Some people say their Yorkies only need 4 trips out per day, but I believe these little ones (mine are 8 and 6 pounds) need to go often. In fact, I believe all dogs need to go at least as often as we do.
If I understood correctly, you said the accidents are probably happening during the night. How many hours between the last night potty and the first morning potty? I would try to make sure it isn't more than 6 hours.
Make sure your dog is good and tired when you go to bed. Maybe have a play session, some trick training, and make sure he has enough time outdoors for his potty run.
You are doing the right thing limiting Harley's freedom of movement in your home. This is probably a good idea not only for potty training, but also for comfort -- he doesn't need to "guard" your entire condo while you are at work. Of course, don't keep him in a crate while you are at work. That is too limiting and will cause other problems.
Consider trying the piddle pads again. When was the last time you tried them? When my oldest boy was a puppy, he would shred them when I was gone. Now he is perfectly pad trained. I just added an 8 month old who was outdoor trained and I switched him to the pads.
To pad train, take Harley to the pad when you think he needs to go and use keywords like "go potty." When he does it correctly, praise profusely and give a treat. Throw a party! Do it over and over. You might have to start with a huge square of 4 pads, and make sure they are proper piddle pads scented to attract dogs. You might also consider picking up a remnant of vinyl flooring to put under the pad and to create a larger buffer zone between pad and carpeting.
To clean your carpet, it would be worth your while to invest in a good steam cleaner (I bought mine for under $200 at WalMart). Spray the enzyme cleaner on the spots and let it sit, then use the steam cleaner. Much cheaper than replacing carpeting.
Good luck and best wishes. Be sure to post updates on progress!