Originally Posted by
red
No. Solder melts at pretty high temperatures, it's not possible to heat anything in a normal guitar with passive pickups enough that it will melt solder.
My best bet is the output jack. If that's not the case, you might want to check the pickup selector switch. If you still haven't found the culprit after that, it might be the volume pot.
Large blobs of solder also increase the likelihood of cold joints, so you might want to use some desoldering pump and/or desoldering braid to remove all the old solder and re-do all the connections yourself (one-by-one so that it's nice and easy).