Hi Seaweb,In your fuse box, the "bottom", if you will, of your 15A fuse location is a red wire...... this wire is coming directly from your ignition switch up front. The "top" of this particular fuse is a red wire that leads to connections that go to your rectifier (at this point it may change to a red/white wire and
also has a branch/joint that leads to your solenoid/magnetic starter switch....... which should be a red wire, but again could possibly be red/white.
In your photo, the large cable leading forward goes to the starter. That should be on the left hand post of the solenoid as we are looking at the photo. The right hand post of the solenoid should have the short battery cable going to the
positive post of the battery.... also at the right hand post of the solenoid should be a red/white wire and a red wire which does not have to be connected to anything else.
It sounds to me like polarity got momentarily switched and there's a strong chance your rectifier has been toasted....... sorry

I hope this helps you and does not confuse you. These particular wires are not difficult to track down and work with....... I have learned this and I am really Red/Green color blind for
real.
PS Yes, I can see in 1 of your photos, the regulator is OK..... I see that green wire curling back up to the 1st tab, then white, then black...
~ ~ ~ jaknight ~ ~ ~