I was stuck in rush hour traffic yesterday afternoon with 85 degree ambient temperatures, needless to say my engine temp started to rise. It had risen above the cut in temp for high speed auxiliary fan operation. Guess what, my high speed fans never came on. I did manage to make it home. Upon further investigation I noticed that the 15amp fuse that goes into the speed relay was blown so I replace it.
This morning while I was trying to troubleshoot the auxillary fans, I noticed that the fuse had blown again. I'm trying to figure out where the problem lies. I am also due for a radiator but that's another story.
What could be causing the fuse to continuously blow?

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1995 E420 152k
1991 300D 2.5 348116 daily driver
1992 300E 2.6 196k-work in progress(head gasket)
2002 BMW 745Li 93k