Attention: TDR Forum Junkies 
I've had a thread running in the 911 forum about this, but I thought I would document what happened for everyone.
Alternator stopped charging and then had a few voltage spikes to 18+ volts. Then the tach died and no charge. Then the PCM would not even light the MIL (malfunction indicator light or check engine light). Truck would run but no tach, no charge, no AC, no overdrive, and no trans lockup. First thing I found out was the alternator had blown diodes and replaced it with my backup. PCM at that point was putting out only a couple of volts on the sensor circuits where there should be 5 volts and 8 volts. Second, after a bunch of probing around I found that 12 years ago when the truck was new some of the wires on the firewall were probed with a needle probe to find a 'key on hot' wire for a camper charging cable. One of the wires probed was the 12v supply for the computer and after 12 years the copper inside the wire had corroded most of the way through. This caused the low voltage at the computer. I bypassed the bad wire and the computer was once again turning on the MIL and throwing codes:
23 - intake air temp sensor voltage too high or low
24 - TPS voltage too high or low
36 - torque converter clutch solenoid CKT or trans temp sensor voltage too high or low
Also the wait to start light would come on, the grid heaters would cycle (in 65 degree temps), then start flashing. The trans temp also was on all the time.
None of this made sense so I talked to a tech a my local Dodge dealer and he said that all of these things, especially the flashing transmission temp light, indicated a PCM failure. I ordered a PCM, installed it, and all was well.
Here is what I think happened: The alternator diodes failed which put AC voltage in the system, the PCM got confused and ordered the alternator to full output, and that fried some of the computer and caused the total failure of the bad wire that supplied 12v to the computer.
Alternator stopped charging and then had a few voltage spikes to 18+ volts. Then the tach died and no charge. Then the PCM would not even light the MIL (malfunction indicator light or check engine light). Truck would run but no tach, no charge, no AC, no overdrive, and no trans lockup. First thing I found out was the alternator had blown diodes and replaced it with my backup. PCM at that point was putting out only a couple of volts on the sensor circuits where there should be 5 volts and 8 volts. Second, after a bunch of probing around I found that 12 years ago when the truck was new some of the wires on the firewall were probed with a needle probe to find a 'key on hot' wire for a camper charging cable. One of the wires probed was the 12v supply for the computer and after 12 years the copper inside the wire had corroded most of the way through. This caused the low voltage at the computer. I bypassed the bad wire and the computer was once again turning on the MIL and throwing codes:
23 - intake air temp sensor voltage too high or low
24 - TPS voltage too high or low
36 - torque converter clutch solenoid CKT or trans temp sensor voltage too high or low
Also the wait to start light would come on, the grid heaters would cycle (in 65 degree temps), then start flashing. The trans temp also was on all the time.
None of this made sense so I talked to a tech a my local Dodge dealer and he said that all of these things, especially the flashing transmission temp light, indicated a PCM failure. I ordered a PCM, installed it, and all was well.
Here is what I think happened: The alternator diodes failed which put AC voltage in the system, the PCM got confused and ordered the alternator to full output, and that fried some of the computer and caused the total failure of the bad wire that supplied 12v to the computer.
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