what is the blue connector on the sensor plate for

[ThomO]

There is a blue amp style connector that plugs into the back of the cis sensor plate. Mine is unplugged when I plug it in the only difference I notice is the fuel pump only runs when the car is running as opposed to when the key is on.

Curious as to what it does.

Car is an 83 sc

[timmy2]

That is the safety switch for your fuel pump cut out. It is there to turn off the pump if the engine stops running. It is also to enable the pump relay at start up.

[LuftWaffle]

Thom, you pretty much answered your own question! It's the air metering plate switch. It's job is to only allow the fuel pump(s) to run when it senses that the plate is depressed indicating that the engine is running. I would leave it plugged in. -John

[ThomO]

That's what I figured it is plugged in I was wondering if it had any other functions

Thanks for the replys

[theiceman]

it is pretty amazing that simply unplugging it would defeat this safety device. but i have had my air meter apart and it does look like a grounded signal closes the circuit and would kill fuel flow.

a better design would have been to look for a closed signal after the engine started and open would kill the fuel. therefore if it was left unplugged by accident or if a wire broke, it would not start.

i guess this was the only technology available in the day though

[john walker's workshop]

it's green actually. the blue one goes to the cold start valve.

[proffighter]

Originally Posted by john walker's workshop

it's green actually. the blue one goes to the cold start valve.

On my '81 930 it was blue too, both male and female...

[boyt911sc]

Originally Posted by john walker's workshop

it's green actually. the blue one goes to the cold start valve.

John,

This is true to many CIS engines!!! While it is green for AFS in some cases, they are NOT always GREEN in many cases too. Some have both blue plugs. The AFS plugs should have two (2) brown wires and the CSV plug have yellow wire & red/black wire. Checking the wires is a better way to detrmine which is which rather than depending on the 'green' plug identification method. What happens if you don't have a green plug in your wire harness?

Tony

[tirwin]

I'm only mentioning this for the benefit of others. Long story short, I believe a shop disconnected mine to "help" with a cold running problem as a cheap, quick fix. It doesn't help, it just masks the real problem.

[john walker's workshop]

never seen 2 blue plugs in almost 40 years doing 911s. some green ones look kind of blue but old them up together and you see the difference. some of those plugs break and get replaced with whatever is handy at the time.

[proffighter]

Originally Posted by john walker's workshop

never seen 2 blue plugs in almost 40 years doing 911s...

There is always a first time

[john walker's workshop]

that's not blue, unless you're color blind. distinctly more green than blue. close but no cigar. i can see why you would be fooled though. the plugs on the engine wire loom are also green and blue to match the ones shown, or people would be getting them mixed up more than they do already.

[Peter Zimmermann]

The safety switch is actually there to prevent the fuel pump from running following a collision. And, yes, at my shop we encountered more than a handful of unplugged switches on first-time-in cars.

[ThomO]

Wow my simple question started a big conversation.

Thanks everyone for your responses.

[proffighter]

Just to proof I am not colorblind

Blue:




Blue AND Green

[Two Rivers]

John I think you are being a little modest, Are you sure it`s only 40 years? With the overtime you put in it`s got to be more like 80.

They look { blue green to me.

[mikedsilva]

Resurrecting an old thread.
Could someone explain, as if to a 6 year old, where the 2 brown wires for the sensor plate switch, connect? ie, where in the engine harness do they go?

I'm working with a car, that has had some custom work done to the harness. It turns out, they introduced another wire for the safety switch. Why? Well, the 2 brown wires that would normally go to the switch, were melted, and cut off... after I cut back the black sheath that houses them both, I found the melted section and after cutting that off, they seem fine. Not sure why they would have melted in the first place?

So, now the safety switch plug has 1 lead that gets earthed on the engine with a ring terminal. The other I traced back through the harness, unravelling the tape, and found that it was cut off from the T-terminal that plugs into the chasis harness, near the left cover panel. They have connected to that terminal, and run a wire direct to one pin of the airflow plate sensor switch (the other one being grounded to engine with a ring terminal).

When checking the 2 cut off brown wires, one has continuity with the same brown wires that connect to the small ring terminal on the alternator. Not sure it is supposed to? The other one still has continuity back to where it was cut off from the T connector..

Question; is this ok to leave as is?
What could have caused the wire to melt in the first place?
What do the 2 pins in the T connector, lead to? Is it a simple 12v power and ground?


Would appreciate any pointers.

Mike

[timmy2]

Depending on the year, there is actually either a brown/black (76/77) or Brown/Red (78-83) along with a brown to the AFS connector.
Brown goes to ground at the alternator.
Brown/Red goes to the T plug beside the CDI. (78-83) then to the fuel pump relay.
Brown/Black goes to a single plug beside the 14 pin connector. (76/77) then to the fuel pump relay.

One wire (brown) is used as a normal path to ground when the switch closes (no airflow).
The striped wire goes to the coil at the fuel pump relay that enables it to pick up and kill the pump power when the switch closes on a stall when ignition is on. (Or enables relay on a start)
You can study the reverse relay logic on the fuel pump relay when you have some spare time.

No idea why it melted. “Shyte” happens…

[boyt911sc]

Originally Posted by mikedsilva

Resurrecting an old thread.
Could someone explain, as if to a 6 year old, where the 2 brown wires for the sensor plate switch, connect? ie, where in the engine harness do they go?


(edited

Mike,

I will try to explain where the 2 brown wires for the AFS (air flow sensor) switch are connected. Instead of using the driver and passenger sides, we will refer them as 1-2-3 cylinders side and 4-5-6 cylinders side because our driver side is actually your passenger. The engine orientation will be the same for 911 including 914.

So let’s begin..........The electrical plug would only go in one-way because of the guide/groove configuration. There are two (2) terminals @ the AFS plug, @ 1-2-3 side the brown/red and/or brown/black wire goes to terminal #85 at the FPR (fuel pump relay) socket. The other terminal @ 4-5-6 side with brown wire goes to the alternator @ D-.

The throttle body is isolated from the AFS assembly and the contact or continuity is made between the pin and insulated spring located below the sensor plate. I have not drank my morning coffee yet but my recollection about this subject is pretty much reliable. Hope this helps you in your troubleshooting. The sensor plate is isolated from the throttle body for the switch to work.

When you inadvertently switched the CSV and AFS plugs and continuously start the motor with a fully charged battery, the electrical section near the starter would start to melt during prolonged cranking. If you have an engine test stand, try this experiment and you could smell the burning plastic insulation.......then you would need to order new engine harness from Timmy. I think he knows more (joke)......Dennis, I am just joking.

Tony

[mikedsilva]

OK.
Thanks guys. VERY helpful.

This one is brown and brown/red.
So the brown going to alternator connection is correct.

And the brown/red going to the t connector is also correct.

So Tony, are you saying that if someone connected the AFS plate and CSV plugs back to front, that continuous cranking would / could have melted the AFS brown/brown red wires? Or are you saying that as a result of continuous cranking, heat from the starter motor area could melt the wires. REason i ask for clarification, is that the brown and brown/red wires looked like they had excessive current running through them, hence the melting. Not from the surrounding area...

However, seeing as the configuration is correct in its modified form, likely I will simply put it back together as is and leave the original brown wires disconnected.