It is a very simple job to use the menu on the FT857D to lower the RF output power but I came accross this posting by AA8AF on another reflector which users might find of interest:
'The “brown wire” feature of the FT-857D is briefly mentioned as the
"BATT SENS" on page 32 of the manual in the “Input Jack” section. The
one sentence reference is easily skipped over.
While I haven’t seen an authoritative complete description of what
happens when the BATT SENS is grounded, it does shift RF power to 20
watts and is believed to activate other battery saving features like
display back light timeout, etc.
I liked the concept enough, that when I replaced the stock power
connector with PowerPoles, I wired in a push-lock switch to activate