The fuse in in the block under the dashboard. Third column from the left, third fuse from the top.
I wondered if the problem might be the ignition switch (or maybe the relay) but the fan appears to be the only system with power when it shouldn't have it. Power windows only work when key is ON.
I tried to insert a graphic. I can't tell if it's here.
The pink fuse is the one that has blown...
I did take the truck into the dealer once. They apparently ran the truck all day but the problem didn't appear. I don't know if they got any codes. It has never been looked at while the problem is active. I think I've got about 142K miles on the truck.
I don't know much about what the ecm does but could it "fail", cause the interior cabin blower fan to run when it shouldn't and allow the engine to run normally almost all the time, except when it decides to blow ignition circuit fuses? The last time this happened was at least two months ago so it's hard to remember but I believe the fan was running in ACC while the igniton circut fuse was blown.