try to keep up Stewart ... read the whole thread .
no one needs rescuing .

the right way to do would be to clean up the wiring from key switch , to kill ... to Boyer box
... so that there isnt excessive voltage drop , even when the starter load is added .
the wiring is old with previous owner modifications .

pulling the gas tank to expose the harness... opening the headlight ... pulling apart the handlebar cluster switch
is not a walk in the park
the OP did not choose to pursue this path ... when a wiring alternative presented itself
that is ultimately more convenient .

jumping extra power when the C4 terminal is live ... is a creative alternative ... i think the credit goes to lab .
but this seemingly simple fix ... created some new problems .

C4 is and unfused battery connect ... so i recomended a fuse be added . .. it protects the kill switch
more than the Boyer . .. the Boyer protects itself if it's wired correctly .

the diode prevents power from going backwards into kill and back into the harness ... there appeared to be some unexpected idiot lights
being back fed ... at one point ...
how much power can the kill switch hande ? ... are the old contacts sticking ?
but the diode will also drop 0.7 Volts ... all the time the Boyer is powered from the kill ... I'd probably leave out the diode ,
and let the fuse limit what can pass back into the harness ... if the fuse blows all that is lost is
the extra Parallel Power feed ... when C4 is hot ... and the fix is disabled , back to square one .