I'm soldering for my beta swap! I need a quick answer!
 

Soldering some connections on an engine harness, can I use "silver bearing, electrical" wire to solder? or do I need to buy a copper one?

I honestly dont think it will matter much as long as it bonds well test it out if you can .

The silver is usually just a few percent, compared to 30-40% of the solder being tin with regular lead solder. As long as you can flow it well, it doesn't matter but it's overkill (price-wise) to use silver solder when plain-jane 60/40 will do.

I use silver solder on my solder jobs and have used it on ECU wiring to various sensors in my engine compartment with no problems. Either use solder with flux already on it or manually put that on after you clean the wires real good that way your solder will stick without any issues. I use electrical connector cleaner to clean the wires before hand to remove the grease or dirt from the existing wires.

Unless a wire is really nasty or really delicate, I'll use rosin-core solder and let the flux inside do its work. If it needs a little extra cleaning, adding a little extra solder (with flux inside) very often does the job.