Would it mess up anything if I ran some wires from my 05 Lionel 4-4-2 main pickup back to the tenders wire pickups so it won’t stall in long switches?
No. It will accomplish exactly what you want it to. You should need only one wire.
And would that be one wire for the center pickup?
Check out last issue of CTT.
Yes. You could use a second wire to connect the frames; but it would add very little benefit.
The article that Frank mentioned is on page 58 of the (current) September issue. It describes using an automotive “bullet” connector. This will certainly work, but is unsightly enough that they show it hidden under the car, held with double-sided tape.
You can make an easy and unobtrusive single-wire tether connector from a male-female pair of connector pins (not the connector–just the pins). Solder them to black wire and cover all but the business end of the male pin with black shrink tubing. Put the female on the locomotive so that you can test-run it alone with out having the loose end fall on the track and make a short circuit (as I found out the hard way).
I’m not familiar with connector pins.
Some types of connectors have loose pins which are intended to be soldered or crimped onto the wires, then inserted into the connector shell. I’m talking about a pair of these loose pins, used without any shell. Molex types are probably the easiest to find. However, I use high-quality gold-plated pins from a large stock that I salvaged years ago. If you would like a few, just let me know, and I will mail some to you.