Electrical Problem

Have a strange electrical snag on an ST70.I have recently refitted the original loom after a restoration. I was careful to make sure all connectors were a good fit and that the colour codes matched.The rectifier was replaced and checked out on test. On this bike the red lead goes to the positive symbol on the rectifier, and the white to the a/c wave symbol. My problem is this. I have power to the brake switches, neutral light and horn but not to the main light switch. Yes, I checked to see if it is earthed, it is. Now this is the strange bit. If I reverse the leads to the rectifier (not recommended as it starts to get hot!) the head light switch functions and we have lights. I've looked at the wiring diagram too many times for comfort and can't fathom this out. The bike is a1979 K3 by the way. Any ideas greatly appreciated as I am stumped!
Regards,
Pete.

Could be a falty earthing issue, probably on your main switch.
These problems can be hard to tackle...

It would seem that the polarity of the replacement rectifier is opposite to the original. Now trying to source the Honda unit.
Pete.