Did you check the battery voltage under charge?

If the battery was discharged for long time, it may be not working properly under load, or it may have developed black wire syndrome affecting the switch and/or contacts.

You could also try a good battery and by-pass the switch and see what happens.

Copied from:

http://www.futaba-rc.com/techsupport/techtips.html

"Black Wire Corrosion.
Over time the battery's negative lead, which runs through the switch harness to the receiver, will corrode. The copper wire loses its bright, "coppery" look and turns almost black. It also becomes brittle and inflexible.

The cause? Storing your system in a damp place with the battery installed. If you leave the wire connected to the battery, surrounded by environmental moisture, an electrical effect results that promotes corrosion of the wire. The corrosion starts at the battery pack and works its way toward the switch harness.

The air doesn't have to feel particularly humid to qualify as a damp environment. Storing your system in a shed or garage leaves it vulnerable to enough humidity (such as the moisture brought into the garage by your car) for corrosion to occur. It will happen even faster if the battery is not maintained and goes flat. Charge and cycle your battery regularly to prevent or slow down the corrosion."