Lead Free tinning on MMM?

[redshift]

I have a V3 just purchased, trying to solder a Dean's on and it won't fuse. I have a 60W iron and already cut off the pre-tinned ends. This MMM is one that has the hardwired battery leads (must say I'm not crazy about that and wonder why that was changed...).

So, I cut off the ends assuming it would be lead-free, and the wire itself does tin fine with lead solder. Did I contaminate the lead tinning I did on the Dean's when I tried to join it to the wire? It will not fuse even though the solder flows perfectly between.

I'm about ready to use a screw lug here, help please!