I just realized I had a bad battery. Being sunday afternoon I just recharged the batteries and figured I would deal with it on monday. Monday I removed both batteries and alt. I figured I would have the alt. checked to make sure it was in working order. Alt. showed a low / puslating charge, so I purchased a new one. With a new alt. and 2 new motorcraft 850's that had 12.8 volts I went home and installed them. It fired right up, better than ever. I checked the system and it only shows 12.9 volts at the batteries with the truck running. The alt. shows 12.9 at the terminal. The alt. bench tested fine. Does anyone have any suggestions?