headlight out/RLU Bypass

[clyderider]

Hello everyone,I searched the past treads and got confused.I have a 79xs1100sf has a new fuse box,fuses are good but,my headlight went out completely.Now I'll have the battery checked again yet tommorow,but whats the deal here? rarely does the actual lamp go out (rarely i said) so it's gotta be wiring or alternator or what? could someone run down exactly what needs checking and in what order without alot of bs like 1.check battery 2 check???? etc.etc.help please!

[bikerphil]

headlight

Hook a voltmeter to the battery while running the engine at @ 2500 RPM. It should be 14.5V. The headlight relay won't trigger if the alt. isn't working. Tach also won't work. Try cleaning your alt. connections if it isn't charging.

[mro]

If the fuse, bulb are good and the alternator is working, most likely the head light relay went bad.

It's under the tank, about an inch and a quarter square and has a 4 wire plug going to it.


mro
BTW, can pull plug, put a "jumper" between blue and red wires and head light will come on/off with the key.

[Crazcnuk]

"rarely does the actual lamp go out "

It's the first thing I would check. They may go out rarely, but less rarely than any other component in the system.

[TomRodgers]

Mine went out also...with the vetter fairing on it, i just "hot wired" the light to go on with the ignition, just dont have low beam...

have been told (read it on this site) about the RLU box that fails...

going to try and bypass that and see if it works.

[clyderider]

headlight out

Ok I rechecked the fuses put new light in and a light relay box from twin bike still no headlight have'nt checked battery yet but it's running the bike and all other lights work what can i do now????? help gurus!!! please!

[mro]

put a "jumper" between blue and red wires and head light will come on/off with the key.

The wires are in the plug that connects to the relay.

If this works then there's a problem with the relay, AC generater, the diode on white wire to relay from AC generater or a bad wire between above. Can check the white wire for voltage only with bike running, when bike running generator powers white wire to activate relay. (the relay is just another type of switch)

If above works not, then check fuse and red/yellow wire with a volt and ohm meter. (Check red wire at relay connecter for 12V)
No voltage there then ckeck at fuse box, then other side of fuse box.

Still can be a few other things but I gota go


mro

[scalded dog]

If you need to check the light itself, pull it off and hook a ground wire to the post on the light that sits by it self on the bottom, then hook a wire to the hot post on the battery, and touch it to the other post that are side by side to make sure the bulb is good, one post is for high beam the other is low beam. If it works then find a hot wire when the key is on, to hook up your light to, I would hook up the high beam then adjust the light to shine down a little more than normal. Later 'Dog

[oldyam80sg]

I put a jumper in awhile ago because when i started to work on the bike in March the headlight didn't work.The jumper idea works and has provided me light.I knew that the lights were working last year and couldn't understand what went wrong in the course of 4 months of leaving it sit.I needed to change the battery because it wouldn't charge.I cleaned the connectors and put dielectric grease on them but nothing changed so i went with the jumper idea.Since then i cleaned the wires behind the fuse box ,and also changed the broken diode and installed TopCats fuse block.Today i went to put fuel filters on the bike and removed the jumper.Now the lights come on as soon as the engine cranks.It took awhile but finally they work like they are supposed to.

[clyderider]

headlightout

Man-o-man what a wiring mess these bikes are! I have a twin bike 79sf in the process of a tear down and I had the opportunity to examine behind the fuse box,you have to really becarefull trying to get at the white wires from the light relay harness.then try and find the burned wire if thats what it is! so far heres where I'm at --checked battery,reserve light relay,fuses,headlight all good now it's gotta be a wire or diode in the white wires me thinks but,what if its not? I hate not knowing and just doing the jump wire red and blue but what are my choices??????uggggggggggg ...frustrating

[Crazcnuk]

When I first got my XS, the PO had a wire running from the fuse box to the circuit that runs the headlight, tailights, etc.

When I changed the fusebox, the lights started to work without that extra wire, so I used it to light the trunk taillights.

A couple of weeks ago I put in the HID headlight, and now ALL the lights (ie headlight, tail, park, dash) will just cut out once in a while?

I feel your pain with the headlight circuit!

I bypassed the RLU, and I am wondering if it may be the relay on mine cutting out while I am driving?

I replaced the relay when I first got the bike, the first one just buzzed.

[mro]

White wire w/diode has voltage only when engine is running so the head light will come on only after the bike has started.

If it does not come on now when engine is running check if your getting voltage on the white wire at the relay.

No voltage and ac generator working, the diode or wire is bad. Will need to unwrap harness to get at where the diode is in wire. Connection could have come loose or diode bad.
I think the diode spec is 50VDC, 1 amp


mro

[Ken Talbot]

Here's what it looks like:



and where it lives:

[clyderider]

headlight

Ok thankyou for all the information everyone.I still have no headlight and am still frustrated but I have decided to jump the blue and red wire to have light.my question is will i only have high beam doing this? 79xs11sf k&npods

[oldyam80sg]

You should have high and low beams.Did you take apart the connectors and clean and put some dielectric grease on them?Did you check the wires and connectors behind the fuse box.I think that is where the alternator plugs into.Does the tach work?If not then you are not charging.Also did you check the diode under the tank along the harness?It is in the harness itself you should see the plastic covering where the diode hides.You might have to unravel the black covering on the harness to find it.If that is bad the lights wont work.Jumping the wires will get you lights but you should look at all the possibilities before you jump them.