Randy,
I looked at your fuel pump that you sent. Below are some pics.
One is a photograph of a rotor wire that is normally attached to the commutator. The other is the end of the wire that was found loose on the rotor.
It appears that it was over-heated when it was originally soldered and created an inherent weakness in the wire. With gasoline flowing around these wires, vibration from the flow probably caused metal fatigue in the wire which may have resulted in failure. Beyond that I have no clue...
Check out this - looks like serious heating - note the increase in oxidation product. Cu is a great catylyst for such - a really good anion transfer participant
Check out the rounded end - if it was cut and not over heated the ends would have two planes from the snip. When it got real hot it rounded the ends (in theory) which would not have happen during the soldering process (I don't think)