If you have an ohmmeter you can check the resistance level for any of the wires. Copper wires turn lite green when they are corroded, it not a good thing but it usually only happens towards the stipped end and a bit back into the insulation. If you have excess wire you should be able to cut some back and stip it again to get to fresh copper. You can use some dielectric grease on the new connection but only after it is connected, the dielectric grease will prevent corrosion but it will also prevent conductivity, so only put in on after the connection is made, or you can shrink wrap the connection, be sure to get shrink wrap with glue on the inside to make a waterproof seal.