89 GMC Jimmy

The Chilton’s manual for the range of trucks that includes mine includes a wiring diagram that is supposed to be year specific. This diagram shows a fuse panel marked ‘Horn’ under the relevant slot, when the stock fuse panel is, in fact, marked ‘Horn/DM’.  What does the ‘DM’ refer to, and more importantly, what all is served by this fuse??

I’m chasing a short that has this fuse apparently directly affecting the operation of both my fuel pump and my dome lights that I’m aware of at this point. This short is probably the direct result of wire overheating due to a much nastier short in the rear loom that I just repaired.