SealClubber, I am quite few years out of physics, but you are talking about "skin effect", correct? I thought that really only started to matter at higher frequencies, well above the levels in a pinball machine.
I thought at pinball machine frequencies the sectional area of the wire was all that really mattered and since stranded had gaps between the strands it actually took a larger gauge stranded wire to give the same load carrying ability compared to solid.
BTW, none of this matters for the OP question. It is only my trying to clarify a memory. I always use stranded for pinball work except for on boards when I am making/replacing traces because it is easier if the wire stays bent the ways I laid it onto the board, but we are talking about some very thin wire for that type of work.
Edit: wow, I am late to my reply. Looks like others commented on skin effect before I could post my question.