77 "D" No Headlight voltage, Where is this resistor located?

Slimbob

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Mostly stock 1977 XS650D.
Pamco Ignition
PMA alternator
SS Reg/Rec

All was working well until I just finished replacing my handlebar switches and installing new speedo. Now there is no voltage to the headlight, hi or low.
Can someone tell/show me where this resistor is that feeds the dimmer switch? According to the drawing in my Clymers book,
There is a (R) red wire in and a (Y/B) Yellow and Black wire out. Can't locate it.
And is it possible to eliminate the RLU and Light Checker completely?
Any help please. Summer is passing by.

Thanks,
Slimbob
 

gggGary

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There is no dimmer or resister. The switch supplies either of the two headlight elements. Check your grounds?
 

jpdevol

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IIRC that "resistor" diode is located under the fuel tank - rectangle cube looking thingy - please verify by wire colors (not my memory).

The RLU can be dispensed if you jumper BU/BK to BU/YW the checker just eliminated.

Verification welcome??
 

jpdevol

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Courtesy jayel & 650Skull via Tech section here
77_XS650D.PNG
 

Jim

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There is no dimmer or resister. The switch supplies either of the two headlight elements. Check your grounds?
Actually... there is.
Sumbich if I didn't believe it either. Look at #30 on the right. The reserve lighting unit sends power to the resistor (via the low beam contacts) if the low beam burns out. From the resistor, a reduced voltage is sent to the high beam.
I guess it was all built in to the reserve unit on subsequent bikes... but the 77 does indeed have a resistor in the lighting circuit.



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jpdevol

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I've seen that resistor (looks similar to an old ballast resistor in size IIRC) referred to as a diode as well, so IDK what it's true function is. Gotta go poke around a manual.....
 

gggGary

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Well I could be wrong....
Don't recall it but there's more n more I don' 'member.
More than a few have wondered about a mystery connector under the tank on some years that had nothing plugged into it.
 

jpdevol

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Yep, reference to resistor on 2nd page attached. Still don't know. I 'member see'in one!

Edit: It's headlight alright, just don't know if it cuts current or prevents direction??
 

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  • RLU 77 HL.pdf
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jpdevol

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Hey Slim, ya there?
 

jpdevol

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Agreed. It is diagramed as a resistor. Seems to be another unnecessarily complex design - don't know why current needed reduced. Another afterthought?

Learn everyday!
 

jpdevol

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Jim - My head hurts and you got answers: So, if that resistor is open (failed), the low beam filament shits, RLU lights dash, sends current to Hi-beam circuit, but power stops at resistor and Hi-beam doesn't work? Until manually switched?:umm:
 

Jim

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It was a safety feature JP. Imagine riding down a dark country lane at night and the headlight dies on you.... on a tight curve no less. This system automatically switched power to the high beam.... at a reduced current so it didn't blind oncoming traffic. At the same time it turned on the headlight fail light to let you know the low beam died.
I've got it set up and working on my SG. and it really works as advertised.
You gotta remember the era this came from. Automation was a "thing" back then. Everyone wanted to get in on it. I reckon that given the tech back in the day, Yamaha did a pretty good job of it.
50yrs on it ain't such a "shiny object" anymore... but back in the day it was a "cool" feature.
 

Jim

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Jim - My head hurts and you got answers: So, if that resistor is open (failed), the low beam filament shits, RLU lights dash, sends current to Hi-beam circuit, but power stops at resistor and Hi-beam doesn't work? Until manually switched?
That's why it had separate contacts on the hi/lo switch... it was only active when on lo beam. Switch to hi and it bypassed it.... hi beam worked normally...like it wasn't even there.
 

jpdevol

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Well.......screw oncoming traffic. LOL
 

Jim

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Well.......screw oncoming traffic. LOL
No... that was kinda the point. When the lo beam failed, the hi beam took over at a reduced current (lower brightness) so you didn't blind oncoming traffic. You could effectively switch between lo and hi, and for all practical purposes it acted normally. Lo beam... or the pseudo lo beam pointing was off a bit, but other than that you can't tell the difference.
 

650Skull

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A lot safer on back country/main/any roads without street lighting and no full moon. I know everyone says to remove/bypass the reserve lighting unit because it will fail one day............i prefer to look at it as saving me in case of a light failure more often than it would fail me due to the unit, possibly/maybe/one day failing.
 

Jim

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A lot safer on back country/main/any roads without street lighting and no full moon. I know everyone says to remove/bypass the reserve lighting unit because it will fail one day............i prefer to look at it as saving me in case of a light failure more often than it would fail me due to the unit, possibly/maybe/one day failing.
Agree Doug. Mine works just fine. I don't ride at night much anymore... eyes are gettin' too bad for that, but I live in a "mandatory headlight" state. It's peace of mind knowing I won't get pulled over for the headlight bein' out.
If it ever fails... it fails. 'Till then it's a nice little safety feature.
 
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toglhot

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I thought the black rectangular box under the tank was for indicator cancel.
 
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