OK
The early '86 had a problem with the wires under the fuse holder burning up and shorting, so you may want to look there first.
The Benz Remedy was they added an aux fuse holder in parellel with that one outside the F1 box and that eliminated the problem.

As posted , you want to know if the fuse is blowing due to load or short.
If you do not have an amp meter, just run the fan direct with a 16A fuse in- line and see if it holds..that will eliminate the fan draw as suspect.

Then you know wiring or connections are bad upstream..also look at the teminals on the R15 pre-resistor. Another common problem spot.

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A Dalton