Something is very slowly draining the battery. Where do I start looking ?

 

Disconnect the neg cable at the battery and use a meter (most cheap meters are fine) to measure the current that the truck is pulling when turned off. I don't know the normal draw for a D2 but others here do. Then pull fuses one by one and see which circuit is drawing the power. YouTube has several good vids showing how to do it.

 

Let Eric show you how...

 

Thanks very much; that's very helpful indeed.