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Old 12-01-2012, 11:47 AM   #1
cas.vanderwoude OP
Joined: Nov 2012
Location: Hawaii
Oddometer: 18
brake light help?

I've cross-posted this on the airheads bulletin board as well, but hoping for aome advice this weekend. I'm Itchin' to get this thing on the road.

Oh mighty hedz - please help!

I bought an R90/6 (1974) in boxes and have spent the last
year or so trying to get it back together. So far
everything is done. It runs sweetly, everything cherry
but... I'm stuck on the last 2 little niggling frustrating
bits before I can get registration and ride off into the
sunset. This forum has been invaluable so far so please
guys help me out one more time? My problems are now brake
lights and horn.

Brake lights:
Rear brake - switch tested, it works and all correctly
connected but no brake light.
Front brake - figured out the indicator wires were missing.
There should be a green/black and green/red going from the

This I can fabricate, but...
My circuit board does not seem correct for my model - no
green/red section (#54?) So I figure I could connect the
green/red running out of the main harness directly to the
front brake switch wire, and the green/black running to #15
on the board? I tried this - no luck...

I have a weird left control switch. It looks correct but I
can not find any circuit diagram for any related model that
matches up:
These are the wire colors:
Green - to board
Red - left loose
Yellow/white - to ignition switch
Green/grey - loose
Yellow - to board
Brown - toboard
Grey - to ignition
Brown/white - to board

I'd dearly like the horn to work (I have twin Fiamms but not
sure how to wire or mount them. Also, if its not too much
trouble, a way of not running the lights when I'm riding.

ANY help will be gladly appreciated and repaid in lodging on
your next Hawai`i visit.
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Old 12-01-2012, 12:25 PM   #2
Beastly Adventurer
craydds's Avatar
Joined: Aug 2010
Location: Las Cruces, NM
Oddometer: 1,167
Here is a schematic I refer to frequently - . The wiring diagram in the owner's manual is most helpful, too.
ABC #12947
'75 R90S
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Old 12-02-2012, 09:53 PM   #3
cas.vanderwoude OP
Joined: Nov 2012
Location: Hawaii
Oddometer: 18
quick update

folks, its all about assumptions. If you have them before trying to fix a problem, well, don't

assumption 1: brake light was not working; WRONG. The tail light was not working and the brake light was on all the time.

assumption 2: the wiring harness is good. It was not.

In the end, I found what must be a short in the harness. the green/red cable was live all the time - even with nothing connected at either end. ran a bypass and the brake lights now work. Haven't yet solved the cause of the tail light problem but bypassed it and now tail light work as well.

Off to the DMV tomorrow! Thanks for all the riders who emailed me with suggestions.

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