Fuel Pump Relay

[Morrie]

Hi Guys,

I have been reading dozens of VERY helpful threads over the past couple weeks trying to both fully understand the way the fuel pump works, and try to understand the reason why mine runs with the engine off and the key in the on position. (safety issue)

Basically, what it has come down to is the connection from the airflow sensor switch to terminal 85 of the fuel pump relay. My understanding is that when the engine is off there should be a short from terminal 85 of the relay to chassis ground, made through the airflow sensor switch.

I've verified that the connector is in place on the back of the airflow sensor switch. I tried jumpering the connector and there is no change at the relay. I figured this takes the actual switch function out of the equation. The connector is a dark green color, which I believe is correct (but not assuming anything)



My struggle right now is to understand where the wiring might be exiting the engine wiring harness and entering the chassis to head up to the front fuse panel. I peeled back the wiring cover and it looks like a brown and a brown with red striped wire. The brown looks like it probably goes to the ground bundle that is screwed to the engine in the drivers side, closest to the front of the car. I am stumped on the brown wire with red stripe. I have tried to hunt down continuity on both the engine harness connectors, looking for a tone on my continuity tester, but no luck.

Here is the kicker- the car is a 76 911S, and the engine is a 3.0 SC motor from an SC, complete with lambda setup. I know I am asking a lot here, but any suggestions here would sure be appreciated.



It's probably unrelated, but I found this connector stuffed down between the air box and the intake manifold just to the left of center. Any ideas on what it is and if it's related?

[timmy2]

The 3.0 engine harness has the safety switch wire run to the white T connector below the CDI box. The '76 body harness has the safety switch normally connected with a single brown/black wire beside the 14 pin connector at the rear of the fuse panel. You need to run a jumper from the white T connector to the single wire. Tach signal for the '76 normally ran to that white T connector but is run to the 14 pin connector in the 3.0 harness if using the 6 pin CDI.
Pm me with your email info if you need a better explanation of the wiring differences.
Is the tach working?

[timmy2]

Looking at your first photo, it may be the wire that is taped up beside the white T connector coming from the CDI harness. Should be the brown/red wire in that connector with switched power to the CDI

[Morrie]

Thanks so much for offering to help. The tach works, everything works, except this. Where I am struggling is trying to find where the T connector is that came off the switch. Can you give me a rough idea where it comes off the engine harness? I will go look again for the single brown/black wire near the 14 pin connector. Does it run to a pin in the 14 pin connector, or is it just in that general area?

Again, thanks so much. Electronics is my background, and I understand how it all is supposed to work, but I just can't find the wires. If I had to I could make my own wires, but I hate to have to do that.... (as in hack up the engine harness with a jumper wire from the airflow sensor switch to the wire on the chassis, assuming I can find it!)

[timmy2]

The '76 has a loose single wire outside of the male 14 pin connector area on the fuse panel. May have a single plastic cover on it.

Here is a photo of how the 3.0 harness should look as original for the whit T connector below the CDI box. The black connector in the photo is for the CDI.
The brown/red from the safety flow switch is with the red wire in the white T shaped connector

[timmy2]

Original '76 engine harness had a single wire coming off it by the 14 pin connector like this one. You need to find what it plugged in to and connect it to the Brown/red in the 3.0 harness.

[Morrie]

Thanks Dennis-

I believe that this is the chassis side of the harness, correct? Do you happen to know where the engine side T connector breaks out of the engine harness? I am trying to chase that down now and it would help to understand where the breakout is relative to other connections. It is possible that its somewhere stuffed up behind the air box in the engine bay, but before I do a partial engine drop to get more space, it would be good to better understand where the heck to start looking. LOL Gotta love dealing with other peoples idea of "right and done".

Morrie

Originally Posted by timmy2

Here is a photo of how the 3.0 harness should look as original for the whit T connector below the CDI box. The black connector in the photo is for the CDI.
The brown/red from the safety flow switch is with the red wire in the white T shaped connector

[Morrie]

Just for reference, here are a couple more pictures of the snarl of wires in my engine bay near the connector. For reference, I am trying to find the wire in the 76 chassis harness that goes to the 82 engine harness. I think the very good pictures above are the 76 engine harness and the 82 chassis harness? Anyway, I am going to unwrap some wires that are taped up and see if the wire I need is somewhere in there.

[Morrie]

Yahoo! I located the chassis wire. Now if I can somehow figure out where the plug went on the engine harness!

[timmy2]

Both pictures are of engine harnesses. The first is of the CDI plug branch for the '81-'83. The second is of the '76-'77 14 pin connector area.

[timmy2]

Yahoo! I located the chassis wire. Now if I can somehow figure out where the plug went on the engine harness!

It is at the white T connector, 0n the '82 harness the brown/red wire in my picture.

Porsche changed the location where it connects to the body harness in '78.

[Morrie]

Originally Posted by timmy2

It is at the white T connector, 0n the '82 harness the brown/red wire in my picture.

Porsche changed the location where it connects to the body harness in '78.

Thanks Dennis. I think you already mentioned that, sorry for being dense. So, I unplugged the connector and tried to measure continuity from either of the connector pins to either of the contacts on the T connector circled below in the picture of my engine bay. No love on either. Also, I did notice that the wire gauge is quite a bit smaller on the wires at the go into the connector on the back of the plate than the ones in the T connector, so from that I gather that there is an intermediate connection somewhere. Is that right? Maybe that is my issue? Again, thank you for your help and patience.

[boyt911sc]

Originally Posted by Morrie

Thanks Dennis. I think you already mentioned that, sorry for being dense. So, I unplugged the connector and tried to measure continuity from either of the connector pins to either of the contacts on the T connector circled below in the picture of my engine bay. No love on either. Also, I did notice that the wire gauge is quite a bit smaller on the wires at the go into the connector on the back of the plate than the ones in the T connector, so from that I gather that there is an intermediate connection somewhere. Is that right? Maybe that is my issue? Again, thank you for your help and patience.

Morrie,

That white plastic connector circled in the picture has the red and brn/red wires do not go to the 14-pin connector. But part of the engine harness. Test the brown/red (white connector) for continuity to brn/blk (AFS switch plug). They should be connected.

Tony

[timmy2]

As I originally posted, you need to run a jumper wire from the Brown/black that you found by the 14 pin connector to the Brown/red wire that runs to the white T connector Tony circled for you.

The brown/red at the white T connector runs directly to the back of the air metering plate connection in the engine harness.
You have to adapt the new harness to the older wiring configuration by using a jumper or by re-wiring the engine harness to have the red/brown wire exit the engine harness like the photo of the '76 harness I posted.

[timmy2]

A 3.0 wiring harness is not plug and play in a '77 or earlier car.
The tach and safety shut off wiring for the fuel pump in '76/'77 cars needs to be modified... Period...

[Morrie]

Originally Posted by timmy2

A 3.0 wiring harness is not plug and play in a '77 or earlier car.
The tach and safety shut off wiring for the fuel pump in '76/'77 cars needs to be modified... Period...

Hi Dennis,

Thanks for your clear direction here. I completely understand. I do apologize if I made you think I was just looking for a connector on the engine harness to plug into the car.

What I was trying to locate was the wire closest to the 14 pin connector that I could tap into and make the fuel pump connection for safety reasons. I will explain in another post where I am at with this, and what I think my two options are now.

Warm regards,
Morrie

[Morrie]

Originally Posted by boyt911sc

Morrie,

That white plastic connector circled in the picture has the red and brn/red wires do not go to the 14-pin connector. But part of the engine harness. Test the brown/red (white connector) for continuity to brn/blk (AFS switch plug). They should be connected.

Tony

Thanks Tony, that makes sense and agrees with what Dennis was saying also. At least I had the right connector (finally- took me long enough, didn't it!)

So, I went out this morning and rechecked this. I have already tried chasing this through the harness a number of times, looking for continuity fron the brn/blk wire on the back of the AFS to any connection on either 14 pin connector or the other connections in the harness. I tested from each pin of the AFM harness connector to each pin of the T connector with no success.

Here is a picture of the T connector as it exits the harness. I unwrapped the tape to see the wires better. All the wires here are considerably larger gauge than the ones on the back of the AFM connector, so I am certain that there is either a splice somewhere, the harness is bad, or modified, or something of that nature. With a hybrid like this done a few owners ago its anybodies guess. There is no brown/ red wire there, the smaller wire is black with a purple stripe. I thought maybe it was faded, but it is the same under the tape.

It sounds like my best/ cleanest option is to get a new connector and wire it with a ground to chassis and the other wire direct to the shutoff switch. Alternately, since this harness already has issues, I can just cut the wire and run a replacement to the T connector and to the shutoff switch.

Again, thanks for the help. I know this fuel pump shutoff discussion has been beaten to death, but the harness issues had me really stumped. If I am way off here, please feel free to call "stupid" on me and give another path.

Thanks again,
Morrie

[boyt911sc]

Originally Posted by Morrie

Morrie,

Is this the picture of the AFS switch plug with a brown and brown/black wires? If not, what are wire color? Keep us posted.

Tony

[Morrie]

Originally Posted by boyt911sc

Morrie,

Is this the picture of the AFS switch plug with a brown and brown/black wires? If not, what are wire color? Keep us posted.

Tony

Hi Tony,

Yes, this is the plug I disconnected from the back of the AFS plate. I read some posts that said it is supposed to be greenish, which it is, but who knows for sure at this point.

One wire is brown, that meters continuity to the block which makes sense. The other wire is brown with a stripe, it is the one on the left as you are looking at the plug from the pin side. That is what I am assuming to be the one that switches with the AFM plate, and that is the wire that doesn't trace back to the T connector with a meter.

When I get home tonight I can try reaching back there and stripping back some more of the insulation to see if the colors are correct or faded, if that helps.

Thanks again!!
Morrie

[Morrie]

Brown and brown with a red stripe, not a black stripe at the green connector.