Don't know what vehicle you have. If the 82 in your member name indicates the vehicle year if the fuses you are using have plastic bodies they bodies melt or distort.

If that is the problem ceramic bodied fuses or the pointed buss type fuses.

What is the amperage of that device you were speaking of?

Perhaps you could run separate wires, inline fuse and separate socket for you
device.

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84 300D, 82 Volvo 244Gl Diesel