The customer reported that he drove the car home and it was running OK, but hot, almost but not quite pegged out. (May or may not be true, but I’ve been storied to before.) When he went to drive it the next morning, it started and ran briefly. Then it refused to do anything else. The dash lights light up as they should, and most go out as they should by either waiting or shortly after the key is turned to start. There is one small unmarked light in the center of the tach that stays on or blinks the whole time. I think it may be a security light, but I don’t have an owner’s manual. I can make the engine crank with a bump starter hooked to the starter solenoid, but it still refuses to start. I hear the fuel pump momentarily. The cranking speed seems normal, so I don’t think it’s a timing belt issue. All of the fuses check good. I switched the starter relay with another. It made no difference. I tried it in neutral and park. That also made no difference. The car has a factory alarm system. The locks open and lock with the factory fob, although the fob is somewhat damaged. This is why I hate electrical issues.
The red dot in the instrument cluster of a Chrysler product of this era indicates an immobilizer malfunction. You may have an invalid key ( the key handle should be grey, not black) or a failing immobilizer module.
If you’re certain you have a valid key remove the steering column shroud and unplug the immobilizer module for 15 seconds then reconnect. Perhaps the immobilizer module will come back to life for a while.
The battery is up as it will crank with the jump starter connected to the solenoid. The starter relay was swapped with another identical one. The aftermarket key does have a black handle, but it had been starting the car until the other day. I have also tried leaving the battery disconnected for several minutes to see if something might reset. I will look for the immobilizer module. What does it look like?
I don’t know if all PTs were equipped with immobilizer systems that year. If it has the SKIM module shown in the diagram there needs to be a transponder in the key. Transponder key handles are thicker than the plan old keys.
As usual, @Nevada_545 nailed it. The owner confessed that his wife went out of town with the correct key on her key chain. He didn’t realize that the “emergency” key they’d had made was not the proper one. Apparently the system did let him start it four or five times. I don’t know why. Now it won’t do anything. I wonder how often this happens. She’ll be back Sunday night to solve the problem.