Your '99 (and ours) came with a 5,000 pound hitch, a loaded 28' stacker will most likely be way over what you can safely tow. I'm over with just my Jeep and car hauler combo which is right at 6200lbs but I've done extensive reinforcement. Pretty sure the frame and rest of the coach is the same as the ones that got the 10K rating a few years later. We've looked at a stacker so we could tow the ATVs and Jay's Cherokee at the same time, there's just no way the numbers penciled out.
The trailer connector may have a blue wire in it but in ours it was only a stub with the loose end tucked away into the bundle. I had to get 50' of blue primary wire and run it through the bays then do the rest of the wiring under the dash. The brake light signal is easy to get to down at the switch and everything else was pretty straight forward. A 25' fish tape was plenty to do the job, just fun crawling around in the bays.
Welcome to the Alpine group.
The above post is just my experience/opinion which is worth exactly what you paid for it.
'05 Lance 845/'06 F-250 or '99 Alpine 36SDS Usually towing an '01 Wrangler locked on 35"s or moderate '98 Cherokee on 33"s (rear locker only)