Wiring harness confusion when reinstalling my engine

[Hotwatermusic]

I am in the final stages of re-installing my engine. Unfortunately I took so long to do so a lot of the things I thought I would remember, I don't. And in this instance, I didn't take a pre-removal picture. Here's the deal: I have 2 12 pin wiring plugs, one by the rear driver's side tail light--I know that one gets plugged in. But the other one is behind the engine, still driver's side, and I for the life of me don't remember unplugging it when I removed the engine. But I certainly could have. What is that plug for, and should it get plugged back in? The car is a 1974 chassis with an 83 SC motor in it. No O2 sensor, if that makes any difference in this situation. Thanks--I am so close to having this done!

[arbita1]

The plug for the one in the back should be in the back on the shelf by the fire wall. Isn't that it in the picture on top?

[JJ 911SC]

You got 2 plugs, but one is a male and the other one is a female, right?

[Hotwatermusic]

The plug for the one in the back should be in the back on the shelf by the fire wall. Isn't that it in the picture on top?

Yeah, the plug to connect it is there, I just don't recall it actually being plugged in when I droppeed the engine. Is there any chance it was left disconnected on purpose when they did the engine swap?

[arbita1]

Originally Posted by Hotwatermusic

Yeah, the plug to connect it is there, I just don't recall it actually being plugged in when I droppeed the engine. Is there any chance it was left disconnected on purpose when they did the engine swap?

Ah...misunderstood your question.

It's possible. If I remember right (and I should because I just reinstalled my engine a few weeks ago), I believe the wiring harness that the plug goes to is for all the Lambda stuff that goes to the ECU under the passenger front seat.

Do you have an ECU under the seat?

[arbita1]

I just confirmed with the wiring diagrams. The one in the back is a T12 (12 pole) connector which serves the O2 system. If you don't have any of this, it's possible it wasn't connected to begin with.

Also, just for information, the other connector on the left side of the engine is actually a T14 (14 pole) connection. Even though it only uses 12 of the 14 available spots.

[JJ 911SC]

Matt

You beat me to it.

HWM

If you don't remember taking them apart, I would probably leave them separated and see what happened.

[Hotwatermusic]

Originally Posted by arbita1

Do you have an ECU under the seat?

Yes, I do have an ECU under the passenger seat. No O2 though. I just made my first attempt at starting the car, with and without it plugged in, and it won't start either way. Sounds like no fuel getting through the CIS.

[arbita1]

Originally Posted by Hotwatermusic

Yes, I do have an ECU under the passenger seat. No O2 though. I just made my first attempt at starting the car, with and without it plugged in, and it won't start either way. Sounds like no fuel getting through the CIS.

I would recommend you plug it in. The frequency valve needs to be hooked up even with no O2 sensor. My car would not even run without the ECU disconnected.

Chances are it just popped off by itself when you were lowering the engine. The bentley and 101 projects book both forget to mention this connection. I caught mine because I happened to see it in the back while I was lowering the engine. Then I remembered reading some posts reminding people not to forget it.

Plug it back in and then start troubleshooting your no start problem.

[boyt911sc]

Originally Posted by Hotwatermusic

Yes, I do have an ECU under the passenger seat. No O2 though. I just made my first attempt at starting the car, with and without it plugged in, and it won't start either way. Sounds like no fuel getting through the CIS.

Hotwatermusic,

Do a FP test and see if the FV is vibrating at the same time. A fuel gauge will tell you how much fuel pressure is in the system. BTW, fuse #18 supplies power to OXS relay. These are the basic tests. Keep us posted.

Tony