Yes....but I would look around for an Aux fuse holder first...not many still have or use the original #12 fuse....
If you want to be sure and also check if it's the Ignition sw. [ b/c you mentioned that], just bring a jumper wire from the battery Pos + over to the #12 fuse and then retry the fan.. That will eliminate the IGN. sw feed possible.

Looking at your chassis schematic , the exterior Aux fuse modification was Factory after VIN end # A292112, year 1986.. Then they went with Aux Fan feed fuse F15/AUX Holder set up. 30Amp. Look over by the shock tower..Should be a link type fuse. That feeds the RED at the plug behind the Booster............

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A Dalton