CharlieB

In the engine compartment of my 80SC is the junction and connection for the single black wire from the oxygen sensor and the green wire going the relay and control unit under the passenger seat. The single black wire from the oxygen sensor has a female end with a rubber boot. The green wire passes thru a plastic-like bushing with a metal male end. On my SC when installing a new oxygen sensor the green wire pulled out of the bushing and broke off at the male end connector. The bushing itself crumbled apart. The green wire has center copper strands and a second surround of copper strands outside like the ground strands on a TV cable. The green wire was soldered into the metal male end. Can I clean out the old solder, strip and insert the green wire and re-solder the male end? Do I need the plastic bushing/insulator? The wiring shows the green wire going to two points on the control unit so I guess the inner and outer copper strands of the green wire should be soldered together into the male end connector? I'd appreciate some guidance!!

psalt

Charlie,

My diagram shows the central conductor is the signal wire that goes pin 2 on the OXS Control Unit and the copper surround is the shielding and connects separately to pin 4. You need to keep them apart and isolated.

CharlieB

I agree that the main signal wire (green) goes to pin 2 on the controller and that the copper shielding connects to pin 4. But where would the copper shielding connect to on the other end in the engine compartment? The main wire goes thru the plastic bushing and into the male connector where it's soldered. The male connector has threads for screwing back into the bushing. It doesn't just push in the bushing. I'm using the term bushing but it may be an insulator!

psalt

Yes, I think you got it.

arbeitm

The plastic (male) connector on my car is broken. I just got a replacement one with wire attached from a parts car yesterday. I'll have to take a look at mine to see how it's connected.

I didn't even realize there were two conductors in there. I thought it was going to be an easy job of splicing the wires.

Peter Zimmermann

I remember struggling with this issue, but I also remember that the current flow chart for the OXS system was in black & white, so we were never sure what to do with the shielding. As psalt stated, the core wire (green) is the signal wire; I think that, because we were never able to buy a replacement connector, we took the end off the oxy sensor wire and did a male/female wire repair based on that. psalt is correct, the two wires (insulated & shield) must be kept apart, I have a hunch if you open the oxs wire that you'll see what you have to do. My own connector ('82) is hanging by a thread, if I get some time later, or tomorrow, I'll take it apart and see what's needed. I was initially thinking that we made the shielded part into a ground, but I don't think that's right. You might want to try to find "Lorenb", a Rennlist poster who owns Systems Consulting, and he does have a web site.
Pete

CharlieB

Thanks guys for all your help and interest. In the grand scheme of 911SC things this may be a small issue but it sure is interesting!! I think the green primary wire goes to pin 2 on the control unit and the shielding goes to pin 4 according to the diagram. Since we all know where the primary lead eventually goes, ie to the OXS sensor, the question is, I think, where the heck does the shielding connect. Pete, that black wire coming from the OXS sensor sure is mighty thin, you sure you want me to cut into it?? There's a picture of the little devil I'm talking about on page 30, photo 10 in 101 Projects. You can see the round insulator with the male connector sticking out. Thats what the green primary wire runs through and is connected to. The question is how!!

Peter Zimmermann

Charlie: Yeah, I know, but I just can't remember how we fixed the small number of damaged ones that we came across. I've never done one myself, which is part of the problem! That's why I suggested trying to find Loren first.
Pete

porsche930dude

i was going to ask this same question. When i got the car it wasnt connected at all no connector no nothing. so i just soldered the sheiling and the core to the oxs wire. Should i make it so that only the center wire goes to the oxs? If so where does the sheilding go? i guess thats what you guys are trying to figure out. my brain isnt functioning very well today

theiceman

I am not sure exactly what you are talkking about but I can tell you from an electronics principle sheilding is usually only grounded at one end ( and I would imagine this to be pin4 ) the idea is that any field effect signal hits the shielding and goes to ground. Usually when you ground the shield at both ends you can get a ground loop.

arbeitm

So are you saying the shielding would not be connected to anything at the plug side? It basically just wraps the wire and goes to a ground?

theiceman

I am not sure for your particular application how porsche designed it, but in general that is how sheilding works.

CharlieB

I agree that the shielding going to ground at pin 4 makes sense. The primary wire carrying the signal from the O2 sensor to the control unit is subject to all sorts of electrical activity in the engine bay. It runs close to the CDI and other electrics. The signal from the sensor is of such low voltage that it wouldn't take much to disrupt the signal and in turn screw up the control unit functioning. Another thought is that the hole thru the plastic bushing doesn't look big enough to take the whole primary wire and the shielding together. Also the male plug had a stub of primary wire left in it when it snapped off and no shielding was attached to it at the solder point.

theiceman

I just checked the schematics in the Bentley doh ! ..... I have a 78 with no O2 sensor . The Bentley shows what we had figured , terminated at the pin 4 but not at the plug end.

arbeitm

Ok...so basically we are saying you could splice the green wire together (if you got another plug cut off from a parts car) and just leave the outer shielding alone. Am I right?