Dim glowing headlight warning light

79XStLouis

79XStLouis

XS650 Enthusiast
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I have a 79 model. I noticed tonight in the dark that the headlight failure light on the vertical instrument panel was glowing very dimly. Any thoughts on why this is happening? There is no issue with the headlight, so should I disregard this as some low level parasitic draw or try to correct it. If so, where to look?
 
mrtwowheel said:
Check to make sure that there is even a bulb socket in that space, I'm thinking that the bulb has been pulled out of the space leaving an empty hole and you are getting a glow from some other bulb. Maybe not.

Scott
Click to expand...
No, I had it apart and thare is a bulb in there. Nothing lit nearby to spill over either...it's that bulb. Hard to see in the day, but in the dark it's getting some juice. Odd...
 
The power for that bulb comes from the reserve lighting "black box" Not much you can do inside that but I would open the connector a time or two look for corrosion use a bit of contact cleaner, also check the connector in the headlight shell and double check any ground connections in the shell. Check battery ground strap, engine grounds at head engine mount etc. My gut feeling is it's a ground issue. Are you running a stock headlight bulb? My headlight checker bulb glows when I have an LED headlight bulb installed. The RLU is looking at the amperage draw of the headlight bulb to decide to swap to the other element so any non stock bulb may make for funky operation, somewhere there is an easy jumper out how-to to eliminate the reserve lighting unit.
This circuit diagram is from the later specials not sure if it's identical to your 79, Special?.
lighting circuit specials.jpg
 
Check it with the rlu unplugged. It's supposed to get power from there but in broken mode could be coming from anywhere... Right way to approach it would be with a meter you'll find some real low voltage on the bulb -- just keep tracing it back up the wires until you find where it originates. You can unplug various things to isolate them.
 
gggGary said:
The power for that bulb comes from the reserve lighting "black box" Not much you can do inside that but I would open the connector a time or two look for corrosion use a bit of contact cleaner, also check the connector in the headlight shell and double check any ground connections in the shell. Check battery ground strap, engine grounds at head engine mount etc. My gut feeling is it's a ground issue. Are you running a stock headlight bulb? My headlight checker bulb glows when I have an LED headlight bulb installed. The RLU is looking at the amperage draw of the headlight bulb to decide to swap to the other element so any non stock bulb may make for funky operation, somewhere there is an easy jumper out how-to to eliminate the reserve lighting unit.
This circuit diagram is from the later specials not sure if it's identical to your 79, Special?.
View attachment 112698
Click to expand...

i like that schematic Gary it actually shows the internal connections of the components which makes it a whole lot easier to troubleshoot.
have you perchance got a good quality image or scan ? I'd like to get it printed and laminated
apologies for off topic:hijack:
 
Yes, this 79 Special has all original bulbs and electrical components. I read once about disconnecting the RLU and simply jumping the wires to bypass it. I will check for sketchy grounds and connections in those circuits. There is something feeding the bulb a low draw. Many thanks for this thoughtful troubleshooting. You guys make owning these classics a joy. I have owned a lot of bikes, this is my second XS, my first was an 81 Special, and it was actually my first legit street bike. I have to say the XS has a can-do utility to it that most bikes don't muster. It is exceptional at nothing, but damn good at everything. I really enjoy that about it.
 
gggGary said:
um I just did one above? LOL. that's a shot from the J-K manual
Click to expand...


chrikey..... is that the best image you have G:rolleyes:? I can't even make out the wire colour key.
Reckon its about time someone redrew that diagram .Might have a go in Coreldraw

Gary just noticed that it has combined Reg Rec so it is probably 80 schematic not a 79 special ll anyway? yes it must be 80 as it also has a clutch cutoff relay and the 79 doesn't have one of those either
 
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The RLU is known to go bad, and when it does, all sorts of wonky things can happen. Honestly, it's one of the 1st things most of us eliminate. You do need to jumper a wire when doing so though, or the headlight won't work at all. Details are here .....

http://www.excess650.co.uk/tips & tricks.htm

I would disconnect yours and install the jumper wire. If that fixes the problem, your RLU was probably on it's way out.
 
5twins said:
He said it's from the XS-J manual. That would be a 1982.
Click to expand...
"This circuit diagram is from the later specials not sure if it's identical to your 79, Special?."
Read twice, criticize (not)once? :p
I have manuals up to 77 and the J-K They are nice because they do the circuit breakouts, easier to follow than the big wiring diagrams. I'll get right on finding a 78-79 version so I don't mess up again.
 
peanut said:
chrikey..... is that the best image you have G:rolleyes:? I can't even make out the wire colour key.
Reckon its about time someone redrew that diagram .Might have a go in Coreldraw

Gary just noticed that it has combined Reg Rec so it is probably 80 schematic not a 79 special ll anyway? yes it must be 80 as it also has a clutch cutoff relay and the 79 doesn't have one of those either
Click to expand...

Surely you have the 79SF/2F wiring diagram. Could you use that in the program to isolate the lighting system?
 
650Skull said:
Surely you have the 79SF/2F wiring diagram. Could you use that in the program to isolate the lighting system?
Click to expand...

yeah I've already laminated the standard schematic but gary's image is the only one I've seen that actually shows the internal connections of the components.
I'm looking for a full wiring diagram not just the lighting .
When I get time I'll redraw the whole schematic and also a set of sub system diagrams for easy troubleshooting
 

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