I just bought a 98 Dodge Ram 1500 4x4. Of course it didn’t do this when we test drove it, but as soon as we put the money down the problem started. When you start the truck, the interior lights start blinking. I thought it was a door ajar warning, but after testing the doors, it doesn’t stop blinking. Sometimes it will stop when you put it in gear, sometimes it starts again. some times it stops for a few seconds and then starts again. So far it has always stopped blinking after we have driven for a little while. It seems like it will sometimes stop when I fiddle with the 4 wheel drive shifter. I have no idea what this is, and my wife feels like we wasted our money. Help!
I assume you are talking about the courtesy lights which may be controlled by the BCM (body control module). If that is the case and the trouble is inside the module then you will need to replace it. You can try getting a used one from a salvage yard or get a rebuilt one. They are a lot less than a new one would cost. The trouble could be with one of the door switches also and hopefully that is the case. Even though the doors may be shut one of the switches could be faulty. Testing on them should be done first to make sure they are really ok and not the cause of the trouble before purchasing anything.
Since the vehicle is pretty old you should consider purchasing a good service manual for it. It can help you find and fix problems like this. Factory manuals are best to get and Ebay is a good place to find used ones for a good price.