86 Ram Van, 318. went to crank it one day, wouldnt crank. jumped it, and while driving down the road the lights kept gettin dimmer and dimmer. came home, shut the van off, wouldnt restart. took out alternator, had it tested, tested fine. put it back in, replaced battery. drove it, same thing. replaced voltage regulator with one off another truck, it would charge the battery as long as i didnt run any accesories. turn on lights/fan/radio, charge wouldnt get to the battery. replaced it with new v/r, same thing. what is going on? what else can i check?