Chevrolet Repair: Reversed polarity, reversed polarity, chevrolet silverado

Question
Hi, I have a 1983 Chevrolet Silverado pickup truck with a rebuilt 305 engine, a/t and all power.  I bought the truck used, so I don't know the full history of it.  However, the truck has run great over the past two years that I have owned it.  Suddenly, the polarity in the electrical system has reversed itself causing all the ground cables to become hot and upon checking the battery with a simple test light, I found the positive cable was "cold" and the negative cable was "hot".  I removed the battery and the alternator and had them bench tested at three reputable auto parts stores, and was told that both were okay...Any ideas?  Thankx in advance!

Answer
Hi Steve.... thats a strange one....check to see if you have any cables that are grounds touching any 12 volt supply....also with the battey out try putting a continuity tester on each cable and see if you have a problem that way... check the battey for a short...if you feel it is reversed...try killing it stone dead and charge it up again....batterys get a sulpher build up inside and when it builds up enough to touch the bottom of the lead plates it can short out...shake it up or just try a known good battery....check all you wiring for any shorts to ground...i have never run across that kind of problem but thats where i would start looking....hope this helps