Truck Repair: Electrical problems with my 97 Ford F-150, ford f 150, reoccurance

Question
I recently had a problem where my gear was stuck in park and my ABS light was blinking.  I had one mechanic look at it and he said that my alarm was tapping into the same power source that provided lines to my transmission and ABS, causing a short.  He replaced the damaged wiring and put in a new power source for the alarm to prevent any reoccurance and everything seemed to work fine.  Two days after I got it back though, I noticed that there was no power at all so obviously it wouldn't start.  After charging the battery, there was power but the truck still wouldn't start.  A second mechanic couldn't pin point the problem with a diagnostic check, but noticed that the AC is staying on when the truck is turned off, draining and damaging the battery; he also assumed that the problem was with the alarm system (A Code Alarm that's wired into the AC and ignition for auto start).  I took it back to the installers of the alarm and had them disconnect the system, but the AC was still drawing power.  Even with the AC disconnected, there was still current present.  My assumption now, as with the alarm technician and second mechanic, is that the problems lies in the ignition system.  Currently, the truck is in the posession of the first mechanic to determine if the wiring he did may be the cause.  What would your hunch be?

Answer
Hi Paul,
Not my area, but if there was a short, it could have damaged the ignition quad drivers, or other internal parts. If you test some of the wires with the wrong type volt meter, you can damage the system, and tapping into a sensor wire for voltage would be a very bad idea.
Just guessing, I might think the alarm caused the ignition problem.
BUT that is from here, where I can't see the truck wires, and the alarm installation.
If it was installed following good instructions, it could be completely innocent, and the problem somewhere else.
Now if the A/C is disconnected, and I assume you mean the compressor, then voltage might be present, but not necessarily current. Current is the FLOW of electricity, where VOLTAGE is the potential, or presence of electricity.
See if there is a compressor relay, which might be stuck, causing the clutch to stay engaged. That could possibly be a totally separate problem from the ignition problem.
One thing I would like you to try, is disconnect the battery from the truck system for a few seconds, then reconnect it.
Van