If you can solder, the most reliable method is to cut the existing wire harness in two and splice in whatever length you need to eliminate any extra connectors. Sooner or later, any connector on a servo extension will start to corrode, the more humid the climate the worse the problem. Unless you periodically unplug and replug any extension to wear off the corrosion, you will eventually have a failure. If you insist on using extensions, make sure they are of good quality;i.e. gold plated pins and adequate wire gage. Avoid estensions when ever possible.