What is this cable?

[NorthernThrux]

I was cleaning up around the engine electrical panel and found this connector (on the top of the pic. One wire in is red/black-dash) seemingly tucked under the panel. Looks like it has never been used. Contacts are shiny. Just want to make sure I didn’t disconnect something in error? Test plug? Or for some other variant of the 1973 911?

[edmayo]

Thats the type plug used for rear window defrost.

[NorthernThrux]

Interesting. I have a fog light switch that lights up when pulled. All the connections are as per the wiring diagram except tne single black line the defrost relay. And I have no defrost relay either, even though I have defrost wires in the rear window. But no wires coming from the window or attached to the pads in the window, which is Sekurit and matches the markings on the side windows, so I think it is original.

So I imagine the defroster was not an option that was installed? But like the fogs, some wiring was in place?

[RSTarga]

It looks like you have the relay in back, do you have the pull switch in front? If you have the wired rear window you must have had defrost at one time unless someone replaced the rear glass.

[edmayo]

Do you have wires the width of the glass or just a few wires in the middle. Wires in the middle only is a single stage defrost and uses the round black relay, wires through out the entire window is a two stage defrost and uses a large silver relay right next to the MFI shut off relay. If there are no wires coming from the rear window it means someone was too lazy to go to the trouble of putting them in. I've never seen a lwb that didn't have rear defrost,,,have seen lots that weren't wired back in when glass was out!

[NorthernThrux]

I have the full width of wires top to bottom and left to right. And I have a single stage pull switch that lights and has the right wire colours on the back for a single stage defrost (according to the wiring diagram) except it doesn’t have the single black wire that would go to a round relay in the back, nor do I have that round relay. But I do have 2 silver boxes, one of which is the mfi speed relay, and the one in front of it (towards the driver) is the two stage relay for defrost as I’m now figuring out.

This is the way I bought the car looking at the old pictures, so even though the rear glass was out for the painting and a new seal, that’s the way it was put back together I guess. Going to have to remedy that. Kroon, here I come!

Fortunately I have a mint condition two-stage switch in my parts stash ;-)

[NorthernThrux]

Last question for the evening. How do the defrost wires get from the rear window to the relay?

[Simonjjb]

Last question for the evening. How do the defrost wires get from the rear window to the relay?

They come into the rear engine are from the left drivers side window seal. The second picture showed the red/white wire in the compartment near the fuel filer. Its partially in a conduit.

[RSTarga]

Unfortunately even if you have all the wiring in place, it might still not work. The factory used a painted on defrost on the early cars which tends to oxidize and fail. Newer models had the defrost sandwiched in the glass, at least on the coupes.
You would need to check continuity at the wire hookup points on the glass.

[NorthernThrux]

OK. I found the hole on the back deck that comes out by the left engine lid hinge. And I have 220 ohms between the two contacts I did find behind the seal. Painted defrost indeed, so likely all original. One contact towards the top left side and one towards the bottom. I’ll look under better light tomorrow. So it is promising.

Thanks for the help. Love this place.
Ravi