thank you Neil and David,

- Neil - My first thought is those 2 fuses at 9,10 are bad...  as bad as in
quality not meeting the specs as they should, the fuses are from Bussmann
brand (Eaton)

- David - it's a very good theory, excellent even...  thank you - When I
look closely at the base of the fuse holder where the fuses 9,10 sit,
there's no sign of heat damage but the fuse's casing is melted. The idea of
the 2 wires insulation chafed against each other is very probable because
the heat damage is behind the fuse box and the fuse box is in pristine
condition as if nothing ever happened.

thanks again,

dan

On Wed, Sep 30, 2020 at 5:25 PM David Beierl <dbeierl@gmail.com> wrote:

> The ground wire gets hot, melts the plastic
>> sleeve, touches the 86  (+) wire and short everything.
>>
>
> This is backwards.  The ground wire from the relay only carries about 200
> milliamps -- a 24-ga wire would be more than enough electrically.  I think
> your insulation chafed against the 86 terminal and shorted the wire to that
> terminal, causing meltdown the next time you run the headlights.  That line
> is not fused -- all four fuses are downstream of it.
>
> Yrs,
> d
>