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I have an 87 TW with a charging problem. I haven't used it much in years but just recently started making it road worthy again. I put a new battery in today and its not charging. When running, the dash lights and tail light are on solid, but the headlight goes brighter and dimmer with rpm's. I have around 12.7 volts with key off, and it drops to around 12.4 when the lights are on/running. Does this sound like a bad regulator? Any other tests than can be done? Thanks!
 

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'87's have a seperate lighting coil for the headlight. The headlight won't operate unless the engine is running, and light output will vary with RPM just as you're experiencing.



This is normal. The headlight system is completely independent of the bike's charging system and provides its own power. Only the tail and dash lights come on when the key is switched to "on". The '87 also has no front running lights and a 1-year CDI. Slightly different critter from the later bikes.



In addition to that the full charging system output doesn't really "kick in" on those early bikes 'til above 2,000-3,000 RPM and drops off to berely maintenece level at idle, which could be what you're seeing. So when diagnosing them take your voltage measurement at the battery under revs. If you're seeing anything near 13.5 volts at high revs your system is functioning normally.
 

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Discussion Starter #3
'87's have a seperate lighting coil for the headlight. The headlight won't operate unless the engine is running, and light output will vary with RPM just as you're experiencing.



This is normal. The headlight system is completely independent of the bike's charging system and provides its own power. Only the tail and dash lights come on when the key is switched to "on". The '87 also has no front running lights and a 1-year CDI. Slightly different critter from the later bikes.



In addition to that the full charging system output doesn't really "kick in" on those early bikes 'til above 2,000-3,000 RPM and drops off to berely maintenece level at idle, which could be what you're seeing. So when diagnosing them take your voltage measurement at the battery under revs. If you're seeing anything near 13.5 volts at high revs your system is functioning normally.




Thanks for the info. I checked again today and I am not getting anymore voltage at the battery when revving the engine. I've actually been driving around a bit, and now its down to 12.2 volts. It doesn't go up at all....only lower
 
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