One way or the other a single wire 6volt yamaha AC regulator has to save 6volt headlight bulbs so long as its mounted to earth & connected into the yellow from the mag. Not sure if that's the right way but grabs the power at source at least. But if you're connecting it into yellow at the bulb i think yellow is high beam so will only save that one--so not the right yellow. I'm woffling & just thinking out loud, so might be off subject slightly.

Single wire from 6v regulator gets spliced into the blue wires (for clock illumination bulbs) in the headlight bucket. The colour of the wire on original Yamaha regulators is yellow with a white stripe, but aftermarket ones might be any colour.

Most common place to mount is on one of the horn mount bolts. Make sure that there is metal to metal contact with the frame to ensure a good earth, or you could also make up your own earth lead, with a ring connector at one end and male bullet at the other, and attach it to an existing earth wire in the same way that I connect the voltage regulator (see next paragraph).

I have attached a link to the Yamaha bulletin that is in the Tech Library here and that has instructions on fitment. Instead of splicing, I have made my own pigtail, with a single male at one end and a double female at the other - put the male into the existing double blue in the headlight, and the voltage regulator and wire that you removed from the existing double, into the females.

Vintage Yamaha Enduro Fans - Service Bulletin #M5-084 re Voltage Regulators (yamaha-enduros.com)

 

Yes come to think, any i did for myself i used to connect into the tail light blue as goes to everywhere including instrument blue & to the headlight in a roundabout way as i think blue from switch goes over to the dipswitch & therefore both headlight beams. Our tail lights are all AC power 'blue' but some US are DC although not sure about back in "71.

"Our tail lights are all AC power 'blue' but some US are DC although not sure about back in "71."

Yes, I believe that, on the US 6v bikes, the tail light blue is a separate circuit (DC) than the clock lights blue (AC) - ie the tail light runs off the battery and the clock lights (and headlight) off the lighting coil, when the engine is running and, in some cases, when the ignition switch is on the second click round.

I appreciate that you know all of this, Morley, but there might be some who don't. 

I should go study wirring diagrams but must be dyslexic or something & have a mental block. But without looking would have thought a dc tail would be light brown like other dc bulbs--i dunno haha. Did wounder though if US models might not have had a dc tail untill they had a better bigger battery to cope with it.

Nope.  US had two blue wires starting in about 1970.  Confusing. 

"Nope.  US had two blue wires starting in about 1970.  Confusing." 

A while back, I was continuity testing a main harness for a CT2/3 that I had repaired and I did have a few head scratching moments wondering why there wasn't any continuity between the front and rear blue wires. Then, of course, the penny dropped that they were different circuits! 

Gr8uncleal, I chuckled reading your thread regarding 'no continuity' between identically coloured wires in a harness. I bought a new aftermarket harness for my DT250 and knew I'd have to make some minor tweeks to it as I was also fitting a Rex's 12v lighting coil and regulator/rectifier.  As part of the understanding process I did full continuity testing of the harness and I like to sketch out my findings so I have an 'as found' starting point to then design my changes around. I'm almost ashamed to say it took me the best part of two days for the penny to drop that my harness had TWO completely separate yellow wire circuits... .  What a wally I felt as over the two day period I'd convinced myself: my meter was dodgy, the harness was wrong for my bike, the harness was a cheapo rubbish one and wires were broken inside, continuity will 'happen' when I start to plug in the peripheral circuit connectors.. . Not to mention my irritation when my missus would ask quite innocently "how's it all going"...Grrrrrghhh !! My brain's mindset was convinced that yellow sheathed wires MUST all be the same wire.  Funny how the brain works (or doesn't  ). Anyway the learning points for me were: keep an open mind, assume nothing, believe what the meter is indicating, and don't take it out on the missus, who BTW is a diamond.

Thanks for posting, Andy.

I also had another brief "senior moment" when testing a repaired harness for a RD400 - both terminals for each wire in the fuse box have to be connected to each other! 

I just read all 59 posts about the headlight blowing problem (which I have on my '75 DT250 6V) and I'm just about as confused as I have always been about Electrics Systems on motorcycles.  So do I just need to get a 6V regulator and wire it in and ground mount it and all should be OK????  Geez you guys, am I just stupid or what???