Headlight works "opposite"

[Nlybarge]

Hey fellas, been a lurker for the last few months as i refurb the 82 XS400 i picked up for 500 bucks. I have replaced fuse box, brakes, all bulbs, tires, tubes, cleaned and rebuilt carbs, painted everything. Essentially, everything i could think of.

Now, i'm down to working out the bugs. The main one i'm fighting with currently (here i should note that the previous owner was in no way shape or form mechanically inclined) is that the headlight works when the key is turned on, but not once the bike is running. As i am understanding it, this is the opposite of how it is supposed to work. Headlight is to stay off until voltage is applied to the relay from the motor spinning, via either initial hit of the starter or kick, which will turn the headlight on until the connection is broken either via the key or kill switch. So, like i said, the headlight turns on when key is in the "ON" position immediately and stays on until the bike fires. From there, Nothing.

I have a relatively firm grasp of electrical systems, but, it is most certainly not my forte. Also, my only electrical tool is a multimeter.

Last thing to note, i could not get the starter button to work. I tried plugging in a spare control cluster with no change. So i eradicated the starter relay and installed a push button switch as a jumper in its place under the seat. I don't see how this could have an effect of the headlight, but, figured its worth a mention.

Any help is very much appreciated! Thanks!

 

[Bedhead]

I would start near the headlight relay and see if anything looks like it was modified. If not, it should have power @ relay on red/yellow wire with key on, ground on black wire, white wire has power only when engine running. Blue and black should only be hot when relay is on. (running engine) Does the relay click when the ignition is turned on? (when the light is suppose to be out)

 

[Bedhead]

Oh, and about that starter switch. You said "painted everything". Did you paint the bars? The start switch grounds through the handle bars. HTH.

 

[DARKMIDKNIGHTWARRIOR]

Welcome to the forum! There are also wiring diagrams on here if you use the search bar at the top.

 

[Nlybarge]

Thanks for the responses fellas. I just got a chance to try and figure this out. I checked the relay, I can feel and hear it click when I plug it back in. I don't see any obvious signs of modifications, wires are a little melted, looks like someone had a starter fluid accident. So, what's my next step? I'm assuming I'm gonna need to follow a wire or two? Which ones?

Also, I didn't point the bars.

Thanks again!

 

[arfstrom]

Here is that wire diagram that we were alluding to. It is really everywhere. That headlight relay, has fuse power going in

• 
  R/Y 12 FUSE POWER IN
  W 12 VOLT POWER IN FROM ALTERNATOR
  B COMMON GROUND
  L/B POWER TO DASH LIGHTING/CONTROL HI/LOW BEAM

So with a multi-meter device, you should have 12 on both the R/Y and W, and L/B So if you have no power on the White line, means your diode is shot, and there is an extensive thread currently 10 pages. check for shorts while doing this test, remember you wont get voltage on the white line while the engine is off. (its from the generator, if the generator isn't running, you will not find voltage) Only ground I see on any of these items, via the diagram is the main post under the seat. Shine that up a little bit too. (both the bike and the brass of the ring.) of course, my experience is on the 81 model. so good luck.

 

[Bedhead]

How melted are the wires? Only takes two wires stuck together to mess with that relay.

Also, as far as the starter switch goes do u show power at the bar switch with ignition on? Should show 12v until button is pushed.

 

[Nlybarge]

Thanks for your help fellas! After studying the wiring diagram, I ended up jumping the red/yellow and blue/black wires and voila! Headlight! So a quick snip, and a twist together, and the problem is solved. Thanks again!