Vintage Cars: no spark, coil pack, spark plugs

Question
at first i had no spark so i replaced the coil modular and my truck ran again so i disconected it to mount back together and hook it backup and now it wont start what could be the problem now

Answer
Having no information about what kind of vehicle we're speaking of, I can't really give you any specific advice.

From your description (coil modular), I'm assuming that this is a newer vehicle with a high-energy ignition. My suggestions would be to check the connection between the coil pack and the spark plugs. Also, I have known coil packs to have had minute cracks in their substrate which will short them out when they are stressed (as in straining to make the mount fit). It is entirely possible you may have a faulty ground as well.

That's all I can think of, in a general sense.