New to this group site.
Bikes I have had the pleasure of holding:
70s Stellar D frame minibike
83 Kaw csr305
79 Kaw kz750
86 Kaw 250 Tecate
85 Kaw gpz550
90 Kaw 750 Ninja
83 Kaw gpz550
88 Yam Xt350
87 Kaw klr250
88 Kaw klx250
88 Kaw 600 Ninja
87 Kaw kx500
92 suz DR350se
85 Kaw zx900 Ninja top gun 
87 Kaw klr650
75 Honda cb200T
02 Kaw klr650
15 Kaw Klr650- still have

Working on a 74 Yam dt250  (A?) For a friend and struggling with ignition-spark .....


 

State your ailment.
Other than bike junkie!

cliff

 from Salisbury, UK.

Have any new non original ignition parts been fitted? There's a lot of junk repro out there.

Yes, 1974 is the DT250A.

Thanks!!

I am wondering if the forums have a library of diagrams...?   I'm thinking a high resolution wiring diagram for 1974 DT250A would help me trace voltage  and check wiring for unintended grounding.   I'm seeing color wiring diagrams online, but they are of such low quality,  they're pretty useless.  It has an aftermarket coil , and the battery has been removed. I was told it was " running last year " ......  but y'all know how that thing goes 

Check the Tech Library (see top toolbar) for service manual. 

Welcome from NZ downunder.
Being points mag ignition there's only one black wire from the mag loom to worry about.
To eliminate all possible main loom or switch faults just connect 'that' mag black straight to the coil.
Only one wire into the coil [talking plug coil of course regardless of the coil wire color.
Just have a way of stopping it incase of an unlikely scenario of throttle sticking open.
Maybe have a way of pulling the wire off or to be able to put your hand or a flat obgect over the carb mouth without air boot fitted.
Ok i'm over dramatising it but i saw an RM400 about 45 years ago head off with the rider hanging on [untill he couldn't], in his case the throttle slide had missed the guide & was on near full song but must've had quite a job compressing the spring to get the cap on.
Anyway--sorry for the essay. Oh, & as others will say--clean the points--first job before all the above i said.

Also, the 1975 and 1976 DT250 wiring diagrams might well be the same as for the 1974. 

No battery needed for spark. Only one wire required.  See RT325's post for excellent info.