Many months ago I bought a fully original 1974 Yamaha dt 250. The only problem it has is that the lighting system doesn't work. I am still having some problems but I would like to get the voltage regulator situation figured out since I blew my original headlight bulb. After doing some digging through forums, I have found the service bulletin that mentions the part number 49b-81910-60-00 to be used as a voltage regulator on the pre 76 bikes. I can not seem to find this part anywhere. What voltage regulator have y'all been using and where can I find it? Thank you.

 from near Salisbury, UK.

A small typo on your post - the part number is 498-81910-60. Later items had different part numbers, but will work fine.

There are some new originals on fleabay, although they are big bucks. I'm sure that there will be used ones as well.

Basically any single wire 6v regulator should work, and these should be available from motorbike stores - I am attaching a link to one such item and store from here in the UK.

DT1, DT100, DT125, DT250 & DT400 Voltage Regulator - Rex's Speed Shop

I have mounted mine outside the headlight - I rigged up small brackets to attach to horn mount and fork clamp bolt. Just make sure that they get a good earth.

To save messing around with splicing the wire, I made up a short pigtail with a single male bullet connector at one end and a double female at the other. Remove one of the blue wires from the meter backing lights from the existing double blue female and replace with the male from the pigtail. Fit the blue that you have just removed into the double female on the pigtail, together with the male from the voltage regulator. NOTE - I added an extra length of wire from the voltage regulator to the headlight bucket.

Some folks have reported success by fitting a 12v headlight bulb instead of a regulator. This could be a cheap way of getting a brighter headlight!

Here's what I used, it's mounted to the horn, be sure you have a good ground. Gr8uncleal has a great point about using a double female bullet connector so you don't have to cut any wires. I think it's the 4.0 mm version available at vintage connections. Had to encase the url in asterisks to get it to take, odd.

*https://www.ebay.com/itm/126647566291*

Thank yall for the help. I think I will go ahead and order the regulator that Pahiker added a link too. Hopefully this will get me on the right track to getting this bike road legal again. Last time was 1993.

Just looking at a pic of a DT250A 1974 with the horn mounted to the steering, & if you intend to mouint it there rather than direct to the frame then i'd be running an earth wire from the mount to the black up in the headlight--well, anywhere to a good frame earth just to be sure. I like those finned regulator bulb savers.