Those wires are insulated with an enamel or laquer coating applied when the wire was made. As long as the enamel or laquer doesn't get scraped or scratched the integrity of the insulation will be OK. I Have some of those signals and found that some of the connections can get loose or break at their connection where the wire transitions to the multi-colored telephone wire. Probably a loose connection under the shrink tubing covering the splice. It could also be in those little connectors too.