Ignition feed to reg/rec

[Le_Fromage_Grande]

True, but still makes no sense to me being brought up on simple Lucas stuff. The red is the output from the reg/rec but must be at the same potential difference as the brown as it's connected to exactly the same place ie the battery.

This is a guess: the sensing circuit in the reg/rec box drains a bit of current, so it’s cut when the bike is parked.

It doesn't, some reg/rec only have 5 wires, the feedback wire is internal to the reg/rec, as I previously said, the feed back wire doesn't need to be switched.

[JackyJoll]

, the feed back wire doesn't need to be switched.

Yamaha, or Rupe, thought it should be.

[Le_Fromage_Grande]

It's not just a feedback wire, it's the main 12V feed for everything on the bike, most older Japanese bikes are wired like this, but it doesn't have to be switched. Most cars have the reg / rec built into the alternator with just a +12V and an earth connection, none of it is switched.

Saying that, there's no reason to change it from how Yamaha intended it to be.

[iansoady]

Now fitted with the brown wire connected and all looks good - c 14 volts at 3000 rpm. A bargain at £15 or so.