Smoked computer/charging system

01 Durango 4.7 Truck does not charge. Replaced alternator, rebuilt ECU (3x), replaced ECU with new, worked for 20 miles and smoked it too. Has been on scan tool. ECU does not provide pulsing ground to the green wire of alternator field. 12V is however on the white/blue. Alternator charges if green wire is grounded. There does not appear to be any current drain on the system and no fuses have ever been blown. No smoke or hot components have been smelled. There is .6v difference of potential between batteryB+ and the white/blue wire at the alternator. The green wire that runs from the ECU to the alternator has been ohmed out and is good. I am 1 1/2 months frustrated and this is getting expensive. HELP!!! Chris