What is a good source for a 68 DT1 wiring harness?  Thanks Stan

DEET This email address is being protected from spambots. You need JavaScript enabled to view it. is the only person I know who makes wiring harnesses for these bikes.  Sells them on ebay, also I beleive.   1968 Yamaha 68 DT1 250 Enduro Wiring Harness Wire Loom NOS Vintage Repro OEM | eBay

+1 for DEET.

+2 for Deet, (his reproductions are perfect) unless you get lucky and find a used one on ebay thats decent.

Deets are better than the original… consider having him add a rectifier connection to the harness. This will keep you from blowing bulbs out…

Dickie Towers published a service letter showing that Yamaha said put a 12 volt bulb in the tail light of the 1968 DT1 to avoid transient voltage spikes, anyone else seen or heard of that, worthwhile to do or not? Also said that intact working instrument lights are an important part of the 6 volt system, such as it is. Opinions are appreciated as my 1968 DT1 education is limited to knowing how much the 68 parts cost.

From my knowledge of the slightly later bikes, a 12v bulb in the HEADLIGHT would likely work, but not in the tail light - they are on different circuits.

Old service letters were probably on a learning curve.

Sorry Letsjet, I was assuming (very dangerous! ) that the spike was referring to the blowing of the headlamp bulb - I have not seen any reference made, here on the forum, to the regular blowing of other bulbs. However, the logic of the letter makes sense - thanks for posting it and I shall save it in my library of "useful documents that I forgot I have!". 

Early US bikes had the taillight on the same circuit as headlight so yes, it's plausible the 12v bulb might help.  And yes, any bulb blowing on the headlight circuit which includes instrument lights can cause a chain reaction and the rest of the bulbs on the circuit to blow. 

Best solution is the voltage regulator update.