I recently did a similar project on the 640, put on a 7" headlight & tidied up the wiring a bit. I now have a mini blade waterproof inline 30A fuse back at the battery feeding a good size wire up to the dash where the speedo unit now sits on an alu plate behind 3 micro relays ganged together in mounting blocks like this one:
http://www.hella.co.nz/3-498-796/pro...elay-Connector
(Beware that the micro relay blocks as supplied by hella have no terminals & the 2 small lanced female spade ones are like rocking horse shit to find - local auto sparky managed to track some down for me)
So one of these relays has been wired in to take the place of the original aux start relay, the next 2 are fed by my new feed from the batt, 1st is switched by the park light then exits through another waterproof inline mini 15A fuse to feed the hot grips, gps etc, the other one is for high beam through another inline fuse. Low beam uses it's original feed.
Also, dunno what the light unit you have is made of, but if it's glass Narva now do a polycarbonate 7" headlight insert which is much lighter & tougher, 'bout $90 though. I used one for my setup.
Cheers
Clint
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