The solder pot will only work with clean, fairly new wire, tinned or not. Typical temperature should be around 260 degC - 450degF. You would need to flux-coat the wire first. However, if the wiring is old and original, you'll have a bear of a time trying to get solder to stick to it. Old, tinned wire generally won't tin properly, because of inherent oxidation on the surface.

You're better off using a decent soldering iron and electronic 63/37 solder with a flux core. Then you'll want to clean the flux off after tinning.

I have had some success finding bar solder on Ebay. I have two solder pots; one holds about 60 lbs. and measures 6 x 12 in. and I use it to solder PC boards. It's got 63-37 alloy. I can populate a PC board and dip it into the solder, and get great results as long as the components are new.

The other is a small 2.5 in. diameter for tinning, and uses lead-free solder for special jobs. Personally I can't stand lead-free as it requires more heat and will only conform to RoHS components. The lead stuff is time-proven and always works well. I also use a liquid flux on everything that goes into the solder.

Old wiring requires some serious cleaning prior to solder. On stranded wires, I usually spread the strands out and use a sharp hobby knife to scrape the outer surfaces off as much as possible. Then flux it up and hope for the best. It is rare that the solder will soak in 100% but considering the old wire, will work pretty well.