Wutz this plug into?

Hey guys....while trying to figure out why she isnt charging (Barn find sitting for years) I found all this stuff!
In addition to the below there is a yellow wire coming out of the voltage regulator that is just dangling. Not sure where that is supposed to go. The wiring diagram I saw showed everything plugged in via harness...no extra wires. 
Any help identifying is appreciated.
1981 KZ750 LTD
 
 
What does this plug in to?

 
How bout this ground?

 
What is this thing? Is it supposed to look like that?

It looks like a PO had some electrical issues.  I'm not familiar with the 750's but you should be able to find a service manual with the correct wiring diagram here.   www.kzrider.com/service-manuals

 

The 81 Ltd model should be the KZ750-H2 & the wiring diagram shows several unused terminals.
There's a 750-4 chain drive manual floating around the internet & should be linked here on KZR >> gold cover w color wiring diagrams.

First two pics show the acc fuse box: white-black is an acc power terminal.
The white-blue acc wire should go to the headlight bucket where there's another acc power terminal.
Third pic is an acc ground & there should be another acc ground in the headlight bucket.
Last pic is either an outage indicator switch, fuel check switch or brake light failure switch: the wiring diagram is showing the latter w yellow, black & green-white wires.  It's melted for some reason. possibly shorted out. ???

Brake light switch: on my 81 KZ650-CSR the brake/warning light at the tachometer comes on whenever the brake is applied. If the Rr brake light bulb burns out, the switch senses the failure & the warning light flashes. You can test the switch by removing the brake light bulb. see manual for specifics.

The voltage regulator should have 3 yellow wires connected to 3 yellow wires from the stator >> routed thru a 6-pin connector.  reg-rec should also have a red/white power wire, black ground wire & brown voltage sensing wire. red-white may not be routed thru the plastic connector. I redid mine thru the connector. 


 

For others troubleshooting...weird box in the last picture is a Brake Light Failure Indicator Switch.
The other two are electrical accessory leads. 
The wire red and white coming from the voltage regulator should be plugged into the positive battery lead/starter relay somewhere. 




This diagram helped..... 81 KZ750H LTD...seemed to match up. 
 

Did you find the 750-4 manual?