Virago Headlight Problem

 So I have an 83 Virago 750.  Headlight will turn on when the key is in
and on, and it stays on during starting.  But as soon as the bike is
on the headlight dies.  The taillight is still on, just no headlight.
I sat on it today and discovered that the light will flicker at almost
exactly 2000 RPM.  More and it dies, below ~1800 and it dies.  But at
2000 RPM it will flicker.

The starter button is rather old and doesn't stick out anymore, but I
took it apart and pushed it out with no help.  I haven't really
checked the wiring out, but this doesn't seem a likely culprit as the
headlight works as long as the bike isn't running.  I tried shorting a
few of the relays, to no avail.

Any suggestions?

 On 10 Jul, 04:31, BaroldG...@gmail.com wrote:

Check/replace the bulb first.

 BaroldGene@gmail.com wrote:

Either buy a replacement starter button and spring from someplace like
PartsNMore or OldBikeBarn, or just drop $45 and get a generic control
replacement at MikesXS.com.

 BaroldGene@gmail.com wrote:

The symptoms indicate a bad connection somewhere in the supply to the
ignition bus.

The ignition bus is not yellow, it isn't a school bus. The ignition bus is
the source of power to everything that works when the ignition key is turned
on.

There are at least two sets of contacts in the ignition switch. One set of
contacts
powers the tail light and the other set of contacts powers the ignition bus
which supplies power to the headlight, brake light, instrument lights, horn,
turn signals, etc.

Typically a red wire will come from the rectifier regulator to the battery
positive terminal and then another red wire with an inline fuse will go to
the ignition switch.

Then a wire of a different color goes back to the fuse panel to supply the
ignition bus. Suzuki always used an orange wire, your Yamaha may be different.
Suzuki always used a brown wire to go to the tail light.

You can follow out the wires from the head light fuse to the headlight
connector and also check out the grounding wire from the headlight connector.

But I suspect the problem may be in the ignition switch itself. I have had at
least three ignition switches get so hot they burned the insulation of the
wires going to them, or melted the solder attaching the wires to the switch.

Why does the headlight work, with the engine off, if the switch is defective?

The burnt contacts have high resistance, and the resistance gets even higher
when the engine is running and the voltage to the ignition bus rises from
12~volts
to 14.5 volts.

The I squared R loss across the bad contacts increases and nothing gets to
the headlight.

Another possibility is that one of the production break connectors has bad
contacts. Production breaks are connectors in the wiring harness that are
there just to make manufacturing assembly simpler. They are rarely ever
disconnected by anybody, not even a $tealer$hip mechanic.

Production breaks will be in inconvenient places, like up under the gas tank.

--
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 wrote:

What steps can I take to determine if a new starter switch is
definitely the problem?  A friend mentioned that it could be a bad
regulator thus causing the light to come on only at a certain RPM.  I
plan to take that off and check it out a bit.  But I am on a college
student budget and can't afford to keep buying parts that don't fix
the problem.  haha.