To answer your question directly, no, there is nothing that anyone would "need" to touch to remove an engine which would have caused your problem. But it's actually worse than that: it's really hard to keep kids out of the truck when no one's watching; there's no telling who was inside doing what, during the time they had your truck.
To add to your trouble here, I'd doubt that even a reliable electrical technician would charge you more than $1500 to find and fix this problem, unless there were parts involved, and then it might reach that limit. I mention this because around here, that's the limit for small claims court (in some states, it's as much as $5000). Most everyone who runs a shop knows very well how much their exposure to lawsuits is and they keep their customers ire well below that limit, just in case something like your problem happens.
Again, around here, lawyers won't touch a small claims court, or magistrate's court, lawsuit, it's just not worth their time. So, you are faced with defending your case to the judge, or magistrate, who will often side with the business, because you actually have to have proof that someone in their employ did something, that you can name/show, etc., and since you're unlikely to have a video of someone actually screwing something up, well...
So you're left with a dilemma: do you sue them and hope to win, expending your time and effort, because you have to learn the law to even survive the first five minutes in court, and they have to do nothing but stand there, if they even show up. Or, do you walk off and bad mouth them to everyone you can find?
If you win in a court case, the court will likely allow them to make restitution, meaning they "promise" to fix the problem. Do you really want them touching your truck, without your supervision after all that? I wouldn't.
I sympathize with your situation. I had this happen to me, years ago. That's why no one touches my truck except me (I do make exceptions, but they're rare).
