Download the manual to help you track down those wire colors:
Dr Dude:
http://mirror2.ipdb.org/files/737/Bally_1990_Dr_Dude_English_Manual_includes_paginated_schematics.pdf

Black Knight 2000:
http://mirror2.ipdb.org/files/311/Williams_1989_Black_Knight_2000_Manual.pdf
(Black Knight 2000 manual doesnt seem to have wiring harnesses, only boards and assemblies)

Perhaps someone can take a picture of that wiring for you...

Here's where they connect in my cabinet. Looks like the same color wires, except the purple with yellow stripes becomes a yellow with purple stripes.

IMG_1167.jpg
IMG_1168.jpg

The wires themselves then split off and go into a bunch of other places, so if you need specifics other than that, it will require some more intense tracking.

Sorry, not totally clear which item the dangling connector comes from (the BK2K head wiring, or the DrD playfield wiring)

For what its worth, here are the purposes of the various wires.

Violet/Yellow is +50VDC (solenoid power)
Brown/Green is Solenoid #15 (Q14) CPU Connector 1P12 pin 8 - Backbox Interconnect PCB 2J4 Pin 15 and 2J11 Pin 2
Black, is typically a ground wire

In Black Knight 2000, Solenoid #15 is for the Magna-save Driver - in this case, It goes to one of those small single relay driver boards (located on the underside of the playfield). It is my assumption, it receives power and drive and then is used as a high current driver (relay contacts) to drive the magnet to ground (via the black wire).

In Dr Dude, Solenoid #15 is for the Big Shot Flasher lamp.

My guess is, that your empty connector is from the head and there is no mating wiring on the Dr. Dude Playfield because there is no need for the relay driver pcb. Additionally, the Violet/Yellow wire's position is therefore not going anywhere down to power the items that aren't working on the DrD playfield (+50VDC).

So, first, you should check to see what the power wire color is going to all the dead solenoids to confirm it is either Violet/Yellow or Yellow/Violet. Then track that wire up to the head and see where it ends up. You will probably have to add a wire to provide this connection to power the solenoids if you want to use that playfield in the BK2K cabinet. 50V Power on the Violet/Yellow wire goes to the Backbox Interconnect Board at J5 pin 10. It leaves to the Insert at J7 pin 3 and the playfield at J8 pin 3.

You are learning that not all heads are wired the same. There are often some unique connections to things like the head insert panel (flashers etc.) as well as specialty circuits to the playfield (AC motors, high current drive devices.).

Sometimes, a wire color is substituted when they run out of a particular color combination. This might explain the change from violet to yellow.

The playfield wire loom is made up of a bunch of sub-harnesses that get combined at the final stage of assembly.
For example:
GI
Solenoids
Lamp Matrix
Switch Matrix

Sometimes, it is necessary to connect wires from one harness to another to feed a device on one of the harnesses from a connector that starts on another harness assembly. This might explain the added connector. But without actually having my head inside the game, or dissecting the entire harness, its difficult for me to answer exactly why they did it.

Since the connector comes from the playfield and there are features that are not working, it would probably be necessary to add the missing wires into the head to provide the mating connector. Obviously, in BK2K, those wires were not necessary or came from other sources contained in one of the other harnesses so the connector was not necessary. Those wires may exist on other connectors with the wire on the other side being missing.

Here are all the pics I took tonight. Numbered the images 1-6.

I think Cactus Jack is correct in describing where they go as at least the Violet/Yellow and the Black go exactly where he said

The Violet/Yellow goes from your connector then first to J12 at pins 6&7 (it loops as you can see in image 2)
Then it comes back down to the power connector J5 on the lowest board (see image 5)
It appears to be labeled 50V

The black wire takes a similar journey and goes first to J11 and makes the same type of loop (see image 4) into pins 6&7 (from top of connector)
Then is comes back down to the exact same J5 place on the lower board and is marked "DGND"

Look close in image 5 and you can see both the Violet/Yellow and the Black wires on the J5 connector

The Brown/Green wire just comes off your connector and goes straight up to J6 where it connects at pin #5 (from top of connector)

Hope that all helps!

2015-09-24 20.50.13.jpg2015-09-24 20.51.15.jpg2015-09-24 20.52.27.jpg2015-09-24 20.54.51.jpg2015-09-24 20.55.38.jpg2015-09-24 20.57.37.jpg