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Discussion Starter · #1 ·
So my 81 xl500 has 6v AC direct unregulated lighting. Am I correct in thinking Ineed all the correct wattage bulbs to effectively provide some kind of regulation? With just the headlight bulb and tail light the tail glows really bright and soon fails. I see in the wiring diagram there is another bulb in this circuit, the pilot bulb rated at 4w. My guess is this will lower the current to the tail light and even things out?
 

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The should be a regulator there somewhere
 

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This is for a 79 model but shows a regulator for the headlight in fact there are two one for the DC circuit and one for the AC circuit don't know if the wiring on yours has the same colours though probably not

1979thru1981xl250and500_500x357.jpg
 

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Ok I've found another drawing and i was wrong looks like the AC circuit is unregulated but it only runs the headlight and high beam light the taillight is off the DC circuit which is regulated. Measure the voltage at the tailight

1979thru1981xl250and500.jpg
 
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Discussion Starter · #5 ·
Thanks Fred, i will post a scan of my factory manual wiring diagram at the weekend. From what I recall its very similar to your last post but the role of the battery is also to act as a "ballast" in the lighting circuit.
I will measure the voltage at the taillight and let you know.
I have also ordered a 6v ac regulator which I will plumb in to the headlight circuit yellow/white wire.
 

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Discussion Starter · #6 ·
What I don't quite understand is, with the ignition switch "on" but the engine not running the neutral light works but the tail light barely glows. Also the horn just squeaks...
But with the engine running the tail light and everything else works OK. In fact the tail light seems to work TOO well...
So these seem to be powered by the REGULATED dc circuit (Black wiring) AND the battery?

Maybe the reg/rec is shot allowing too much voltage into the black wire...
As Fred says, I need to check voltage at the tail light with the engine running.
Roll on Saturday...
 

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Also check the voltage at the battery and check the battery itself it might need charging or if your overcharging boiled it dry as they say :thumbup:
 

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Discussion Starter · #8 ·
OK boys and girls I have solved it.
Scrutiny of the factory wiring diagram and the bike shows:
  • One coil from alternator for direct ignition
  • One coil from alternator to a reg/rec to charge the battery to run the rear brake light bulb filament, indicators, neutral light, horn etc.
  • One coil from the alternator absolutely and definitely NOT REGULATED to headlight main/dip and tail light filament of the rear light.
I attached this little 6v AC regulator to the unregulated AC feed to the rear light. I bolted it to the frame and for good measure ran a wire from that to another good earth point.
The 6v regulator seems to have done the trick, the lights work as well as you would expect still but the tail light does not go pop with engine revs.

Universal 6 Volt AC regulator - Rex's Speed Shop
 
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