The Delanair 111 system on my car has 4 plugs. The grand piano has 6 ports. 3 on the side and 3 on the underside. I have the 3 plugs on the side connected but the 4th plug has 2 wires (pink and grey) and has to be connected to one of the three ports on the underside. The 2 wire plug can fit into any of the 3 ports on the underside of the grand piano.
Can anyone who has the Mark 111 system look at theirs to see where the 2 wire plug is connected?
Here is a photo of mine.

Thank you.

 

I know we talked earlier - but I just noticed it looks like something might be written in blue ink on that plug. Can you make out what it says?

 

I just looked at my 87, and it only has the connectors plugged into the bottom. The side doesn't have anything plugged in, nor does any connector have only two wires. And my system is working correctly.
But I'm confused. What car is this on? Your 85 should have the MkII system. Is this a later car, or maybe not an XJS? I know they added functions in the later years not present at the introduction of the MkIII system.
EDIT: could the 4th connector be added as a repair to make up for a broken connector or trace on the control board?

 

@ jal1234: My car is a 1988 XJS. The 2 wire plug looks as an OEM piece.
@ Thorsen: The 3 plugs that are connected were labelled "T"; Middle; and something I cannot make out. However, looking at the wiring colors on your photos, those are connected in the proper place.
The 2 wire plug is labelled "BACK". All of the labelling was done with a marker by the PO.
I do not want to connect the 2 wire plug in the wrong place fearing I may burn up the controller. As I said earlier, the 2 wire plug can fit in any of the 3 available ports.

 

I think the 3 open ports you're talking about are the sets of test pins that are supposed to be open/empty. They are only used for diagnostic purposes and aren't meant to have a plug in them. So that 2 wire plug probably plugs in somewhere other than those 3 ports, unless it is a redundant plug as jal1234 suggested. I have an '87 SIII v12 with the MkIII and I can look for a 2 wire plug on mine but I'm away from the car until tomorrow. I'll see if I have a wiring diagram for the MkIII.

 

Thank you Noah.

 

Just thinking out loud - did you trace those wires to see where they go?

 

@ Thorsen: The reason you do not have the extra plug is because your car is a coupe. The Conv is slightly different and has the plug. It comes from the Mode Control Switch and plugs in to the backside of the controller.
I am basing this on the Climate Control wiring for the 1989 MY conv. The wire colors are the same as the 1988 MY conv.
If you have a copy of the S57/58 for 1989 MY, look at Fig 26-2 and you will see the 2 wire plug going to the controller. Fig 26-1 is for the Coupe and the plug is not shown there.
I tried to copy the page but it is not allowing me to do so. Attached is the PDF for the 1989 MY.