1998.5 2500.
When the truck stands for several days (under cover) the batteries drain to absolute nothing (11.2 volts). I have put a test light across every fuse that I can fine in the PDM and in the fuse box under the dash but none of the circuits show a short. If I disconnect the positive battery terminal and touch the cable end to the battery post I get a spark so there is a short to ground somewhere. When I do this I can here a "clunk" sound in the cab (similar to the sound a relay makes when energised) that corresponds to the spark that is produced on contact. Also, with the positive input cable from the battery to the PDM disconnected at the PDM, I get a voltage reading between the cable end and the PDM module terminal. I have removed every fuse and relay in turn but the reading persists. Does anyone have any ideas please? I'm not very knowledgeable when it come to electrics so any help or advice would need to be in laymans terms.

 

try disconnecting your seat harness underneath drivers side, my old gasser had a relay??? in the seat that was doing that, problem is you cant use your seat belt then so im not sure how to fix it but i suspect that could be your problem

 

my 99 is doing exactly the samething, the only difference is brake and ABS lights are on...let us know if you find anything...........thanks

 

I have the same year and had the same problem. It turned out to be that I was in the bad habit of taking the key out at the auxilary position. Even though I had no accessories running it would discharge both batteries in about five days. Everything is "good" now.
If this helps please let me know.

 

I have the same truck same problem.