Strange problem with wipers/radio and cabin temps

I have a 1997 Ranger 4x4 with the 4.0 V6, manual transmission and 130K miles.

My truck has started this latest problem about a year ago and everyone that I have talked to just scratches their heads.

When the INSIDE cabin temp is below say 40 degrees, the wipers and radio will not work. After the cabin temp raises to a rather warm temp, both will come on simultaneously. All other gauges and instruments work fine, just not the wipers and radio.

Please help!