It could be the problem but you probably didn't damage anything.
My polarity became reversed once on the Cadillac and when I turned the key to "ON" ( not "Start"), the generator acted like a starter and tried to spin over the engine.
I used a pair of needle nose pliers to polarize the Genny and it worked and everything was back to normal with no apparent damage. Since then, I always polarize the genny whenever the battery is re-connected.
What do you mean that the truck won't start?
Does the engine turn over at all? Is the battery dead?
Is the battery fully charged but the engine won't turn?
