sooooooooo.... looking at the diagram, the headlight relay is always in series with 2 diodes and the starter relay coil. that would indicate that the light relay is a special monkey right? the lighting relay must operate at a lower voltage and yet current limit enough to keep the starter relay from coming on uncommanded, so I'm guessing it's not an off the shelf relay & think that is an important point. a test as described is ok, but prolly not a good idea to go full voltage too long.
1wizard.... ever test one on a variable power supply to see where it comes in? just curious. I see what they are doin.... any time you push start, it puts plus on both sides of the headlight coil & turns it off.
the Concours had weirder one than that... it used the starter's armature as a generator to engage the rely as it winds down after start, then the relay would latch with alternator power
if I'm answering your question I assume the basic points have been addressed, such as: did you do a compression test? is it still on fire?