Well, I'm trying to sort through some electrical issues with my ute at the moment. Inline fuses aren't polarised, ie they do not have a positive or negative side. They are designed to be placed inline of the flow of current, hence the term inline fuse. The white wire, according to the wiki, connects to the 'A' terminal on the voltage regulator. Therefore, it probably wouldn't be a good idea to connect that wire to the chassis.

I would suggest that you check your voltage regulator and your alternator to make sure that it isn't overcharging, as the more current and amps you push through a wire, the more resistance it creates (yep, good ol R=V/I comes into play here). And resistance, creates 'friction', and therefore produces heat.

The alternator in my ute (was Hitachi LT-135), was playing around on me like this, except I got it before my wires melted. Instead of replacing or adjusting the voltage regulator, I swapped out the alternator for a 55amp Mitsubishi internally regulated unit off of a C20 Vanette, which has an A15 engine, therefore was a straight physical swap with some minor wiring changes. So now, I've got an extra 20amps to play with, and my ute runs better, however I still need to chase down the bad earths that melted my speedo cable.