Hi Folks, I'm looking for a replacement lighting coil for my 74 DT250 and I'm not seeing very many on eBay or otherwise but I see a lot for the DT100. Does anyone happen to know the compatibility across the different models? Will a lighting coil for a 100 or 175cc work for the 250? Also, do I need to have a lighting coil in order to generate spark? I've taken mine out after it failed continuity tests but I'm to sure if the bike can start/run without it. 

Thanks!
Jess

Umm--tryin ta think how to answer. DT100 or any up to 175 lighting coil won't fit as mags are smaller. So what's the problem? no spark!!. Ok i think you're just asking if should still spark without lighting--so, yes it will. Only caveat to that is--on earlier 250's the ignition source was earthed through the lighting coil--never did work out why--to boost spark, i dunno. So if you have a wire left over & the coil isn't earthed to one post screw, then earth 'that' wire. For spark you only need one wire up to the plug coil--black from the mag. If i'm wrong then someone will tell me. Cheers.
Ok, found this diagram which is a year or two later but looking at the source coil it looks linked across to the lighting. & can see the lighting coil earthed. So keep 'that' in mind what i said earlier--will need to earth the source, if that is the case.
yamaha-enduros.com/index.php/wiring-diag...1975-dt250b/download