Definitely +1 on the 100W soldering iron for lamp holders. I've got a fairly beefy 25W iron but it takes f.o.r.e.v.e.r to get the holder hot enough. Fine for doing one. But a 100W iron is the only way to go when you've got dozens of them to do. Judging by the splatters of flux all over the underside of my 4 Bally playfields I'd assume they would have used something similar on the factory production line. No messing!