I have a 1999 Chrysler T&C, randomly the interior lights will blink on and off, the door ajar indicator comes on and dings and the locks will lock and unlock ALL at the same time. This started a year

This is a common problem & is generally caused due to a loose connection of the earthing terminal and 80% the heater module is the one at fault. Remove heater control panel and check multi pin connecter for heat damage which is caused by a loose earth behind heater control panel to the uper left (10mm nut far top right corner of recess). This apparently can cause immobaliser problems. pull the connector plug off. Gave it squirt with contact cleaner and pushed it together and apart a few times to clean it and make a good contact. You will find that by simply banging the dash about the heater and instrument cluster and the car will start straight away. If this does not work, dissconnect the battery, bang the dash, wait 1hour+ reconnect and this will fix the issue 90% of the time.

That sounds like a bad door switch to me. You will have to scan your body computer to find out which one it is. There is most likely fault codes stored for the one that is malfunctioning. If there are no codes, it can be figured out by watching the computer data while the vehicle is moving to see which door switch is acting erraticly.

Also you may want to take a hard look at your battery and charging system. I have seen shorted cells in batteries cause similar malfunctions. Usually, the customer is not aware that there is a problem with the battery or charging system because the engine can start just fine. A shorted battery cell can cause erratic charging system voltages that can cause the computer system to loose its marbles. (Computers do really weird things when they are suffering from malnutrition.)

I have also seen some problems with Dodge Caravan as well as Town & Country where similar symptoms were occuring where the ignition switch had a faulty circuit and was cutting the power intermittently to the Body Control Module (BCM). This type of problem will usually set a code in the Engine Control Module(ECM) that indicates a loss of communications with the BCM.

I highly recommend that you scan your onboard computer network for possible fault codes and verify that your battery and charging system is working properly FIRST before making ANY repairs.