CB740 K4 Low voltage not charging.

[Rosssaab]

Hi there
I've just put a 1974 CB750 K4 back together and she looks and rides great.
For about 10 miles !!
Then the battery dies.
I've tested the voltage at the battery and its only going to 12.4V when revving.
It should be about 14V shouldn't it?
There is a chance I got the two or the white wires coming out the alternator mixed up but I don't think that matters does it?
It's got the separate rectifier and regulator and I'd like to keep it stock but I see there are people saying to upgrade to a combined solid state on for better reliability.
What do you guys recommend?
How do I fit the newer combined one (off a later DOHC Honda I think).
Attached are 3 pics
The first is the replacement combo from David Silver.
The other two are the parts on my bike now.
I see the David Silver part plugs into my existing plug.
What is the other wire in the picture for?

 

[dirtdigger]

Check the connections first, make sure clean and tight. If you get the aftermarket kit it should come with instructions on how to wire it. I have used one off the dohc and it works fine, not that hard to wire it in. Have seen couple of wiring diagrams from people who have done it, should come up easy on a google search.