Hi all, the pre owner left a mess on my bike, he replaced all wires by cables from hardware shop, connected by screw joints
My bike is without CDI. I now bought an aftermarket main wiring loom, whose joined connector to the magneto has green/red, green/white, yellow/white and black/white cables, like I drew in the picture. Found some Magneto pictures in the web, a few only have 3 wires to the connector. Still it´s not clear for me, where which of the cables are soldered inside the magneto.
I really would be thankful, if anybody could help, a am a real Greenhorn in electrics
Sorry for my poor English..., Guido

Hi from NZ. I'm not that flash on difficult electrics but on the older Yamahas DT250 & others, yellow is lights--green/red is charging, green/white is also charging or maybe an alternative rate of charge to the green/red. Bl;ack or black/white is ignition, black in intially to the plug coil then black/white to kill/stop the motor. Any brown will be live from the battery but after the switch. Any red will be battery live wherever it is i think. I found this color diagram which might help--or confuse things more lol. Others will be along soon to help.

I see that diagram was headed up as a 1980 DT250. Think by then the 250 had gone CDI but this shows points ignition so is still relevant to your "75 i'm pretty sure.
Looking on Partzilla DT250 went CDI in"79 & doesn't exist in 1980 on partzilla. Handy link to look at parts for your bike. Drawings are mostly accurate but sometimes get a bit mucked up. Can bring up pretty much any year you want.
www.partzilla.com/catalog/yamaha/motorcycle

I'm pretty sure the 1975 250 would normally have 4 wires out of the magneto.

Yamaha stayed pretty consistent with their colors and what they do.

Black or Black/white out of magneto is for spark and goes to ignition coil

Yellow out of magneto runs headlight circuit

Green/white is daytime battery charging (headlight switch off)

Green/red is nighttime battery charging (headlight switch on)

Service Manual in Tech Library here should have a good wiring diagram.

The challenge with an "aftermarket" harness is they might and often do use different colors than original Yamaha... There was another thread here recently where someone had no turn signals... aftermarket switch harness used different wire colors. Once the owner traced out the functions of the aftermarket switch he was able to get it to work.

DEET makes reproduction harnesses for many of the (US) models and uses the correct colors to match Yamaha if your harness doesn't work out.

yep that diagram shows 4 out counting the black going left to the coil. 3 off the lighting/charging coil.

b=ignition g=day charging g/r nite charging y=headlite w=only use if battery not charging fully (daytime) use w instead of g wire is the way dt3 & others wired Deet sells a mag harness, I got one as my wiring was kaka, its beautifully done!

Hi all, thank you very much for supporting and tips. The light at the end of the tunnel comes closer. But maybe I was not clear about the real purpose of my question. I removed my Magneto and took some pictures. There are 3 cables, coming out of the magneto. For what is the 4th in the connector? Regulator? I learned now from you, which cable color is responsible for which function. Ok so far, but my real problem is, where to braze it. Which color to braze where onto the coils which color to the condenser? Maybe someone has a magneto as spare part and could have o look? For whatever reason the pre-owner destroyed one slot of the base plate of the ignition.
Will become interesting, to find out. But as I got the bike, it was running.
Hope you have an idea.
Regards Guido

look for good wiring diagram here in manuals, has good easy to follow diagram 4 your 75 in section 2

I don't think your wires are correct. is that small black wire u have to ignition black I think is a charge/light wire. The black wire (harness side) should go to points/condenser and source coil all are soldered together for ignition. The other 3 are your charge, nite charge, and headlight/insturment lights on the other coil. Your manual (in electrical section) has some ohm tests that should help you figure which leads go where, just looked it up, coil lead to yellow (wire off coil to ground) will have appx .25 ohm, the g/r will have .35 ohm, and day charge g will b the one w/highest reading, (I think) it was 1.3 ohms, just remember source coil only ignition, (light coil may have a ground wire attached to source coil) study circuit in the factory manual & you'll c what I mean. Hope this helps

You may want to contact Deet for a mag harness, those crimp connectors gotta go, solder & heat shrink r the way to go here