Leave the blue on the black plug alone.

The other end of the wire (yellow?) on your pigtail should go to one of the connections on the existing double blue female. One of tacho/speedo illumination lights goes to the other and the same for the double female connector on your pigtail - what you have shown looks correct.

The high beam warning light bulb can be a pig to remove at the best of times - very little to get purchase on with normal sized fingers! In the past I've had to break the bulb glass and use a small pair of pliers to remove the rest of it (make sure safety glasses are worn!). If it's corroded, then it might be impossible to remove and you're looking at buying a replacement.

Confirmed that I tapped into the blue wire coming from the tach which then goes into a double female connector I added to take the regulator wire. The output from this connector connects to the factory double connector that takes the speedometer blue wire and then outputs another blue wire which goes into the frame backbone wiring harness. The blue wire from the light switch also disappears into the backbone wiring harness. I turned the ignition switch to position 2 and confirmed the tail light activates, so that looks ok. Turn signal indicator light is working, but the other indicator lights are blown, so need to wait for new bulbs to show up. Hoping the 3 blown bulbs(speedo/tach.high beam indicator) may be causing this grief, but doubt it's that simple. Gr8uncleal - the high beam indicator bulb was corroded,unable to remove, so new one is on the way. At least there wasn't much glass to clean up, lol.

Have you tested the resistance figures on the rectifier?