1. Having trouble logging in? Try closing your browser and re-opening it. If that doesn't work, try a different browser or device. The site will be updated soon to resolve these browser issues.
    Dismiss Notice
  2. Dismiss Notice
  3. Hey Facebook people... We've created a group for XS400.com members to connect. Check it out!
    Dismiss Notice
  4. Want an XS400.com t-shirt? Go to the store to order. Limited sizes and quantities available.
    Dismiss Notice

Field Coil wiring question, ground or keyed power?

Discussion in 'The Garage' started by Spitfire_X24, Oct 3, 2021.

  1. Hi all, been away a while, very busy summer and very little progress on the bike, just getting going on the rewire, and ran into an issue with how to wire the field coil of the AC generator. All of the wiring schematics for bikes with the points style ignition with no TCI show the green wire running to the regulator like on all models, but the other black wire coming off the field coil goes to ground. On this bike, it switches from black to brown at the connector and goes to keyed power not ground.
    I’m building my own harness using Drewpy’s steps and I don’t want to mess this up. I’m going to wire it as it is, with the black wire going to keyed power, but every pre-TCI setup I see has it going to ground. Just seems odd is all, there is no schematic in the Haynes manual that matches my bike completely. It’s like a mix of the 1979 US XS400F model, which it is, and the newer G models.
    Has anyone else run into this?
  2. So I think I got this sorted out, but now I'm scratching my head on whether or not my bike should have both a Light switch and a Headlight relay?
    There are no other schematics with this setup, yet my bike has both.
  3. Alright, I found a schematic that has a similar setup to my bike physically, it's the XS400-2E Schematic on page one of the Yamaha XS400 Wiring Diagrams thread. Although the Relay in that schematic is called a "Turn Relay" it is wired the same as my bike. It sends power to the two position Handle bar switch to turn the lights on or off.
    The way I understand it, with the switch off, you start your bike and as soon as the yellow wire from the Generator to the relay gets power it closes the contacts in the relay, and supplies power from the red and yellow (R/Y) keyed power from the fuse box to the blue and black (L/B) wire which then goes from the relay to the handle bar Headlight switch, that wire also runs directly to the HI/Lo Dimmer switch, which means that there is already power there... before you turn on the switch. Oddly, the Red/Yellow wire also goes to the handle bar Headlight switch....It's doubling up the circuit? Not sure of the point of this?
    Unless I'm reading the schematic wrong, but I went so far as to compare it to the circuitry on my bike currently, and that is the way it is set up. I even manually tested the relay, and that is how it works. Can someone explain this to me?

    Thanks for your help.
  4. And just as a note, there are no Diodes in this system unlike the XS400H / SH models which have the white wire coming from the Generator with the diode in it to the relay...
  5. Alright, I slightly modified and broke down the entire wiring system on my bike. I started by moving the Ignition Switch towards the back of the bike. I removed the Headlight relay, the way it was wired, as soon as the bike fires up, the relay closes a circuit that runs the wire to the switch. I'll just leave the switch off until the bike is running, same difference, just manual, but less wires. Other than that, it all seems to be in order.
    The schematics above should be a good easy to ready guide of anything on this bike now going forward. If you wanted to remove the electric start, there's your guide.



Share This Page