WIRING - where does the air flow switch wire go?

[pampadori]

I'm looking for the wire that is on the air flow switch that runs up to the fuel pump relay on my 1983 911SC.
This wire is supposedly Brown with a red stripe and runs all the way to the #85 pin on the FP relay. I no longer have the actual engine harness but the 12 pin and 14 pin plugs are still present in the engine bay. Does this wire connect to one of those two plugs or is there another one that I'm not seeing?

[boyt911sc]

Originally Posted by pampadori

I'm looking for the wire that is on the air flow switch that runs up to the fuel pump relay on my 1983 911SC.
This wire is supposedly Brown with a red stripe and runs all the way to the #85 pin on the FP relay. I no longer have the actual engine harness but the 12 pin and 14 pin plugs are still present in the engine bay. Does this wire connect to one of those two plugs or is there another one that I'm not seeing?

Shaun,

The brown and red wire from the FP relay terminal #85 goes to the engine bay @ white plastic plug: male connector near the engine bay fuse panel and CDI area. This is the chassis side. The white plug for the engine harness has the female connector (this is for the engine side). The AFS (air flow sensor) switch plug is an integral part of the engine harness. So if you don't have an engine harness, you will not find this brown wire.

For your '83 SC US spec. with CIS, you would need four (4) sets of wire harnesses:
a). 14-pin male side for the chassis wire harness.
b). 14-pin female side for the engine harness.
c). 12-pin male side for the engine harness.
d). 12-male side for the ECU wire harness.

Post some pictures of your set up to help us visualize and understand what you actually missing.

Tony

[pampadori]

Thanks Tony. To give you a little more detail on what I don't have the engine harness and why I'm particularly interested in this one wire: I'm in the process of wiring up a standalone efi setup and the computer has a ground output that will activate the fp relay when needed. I was going to utilize this wire from the air flow switch as it has the same function on the cis setup.
I don't recall a white plug near the fuse panel in the engine bay however.
I'll have another look the next time I go by to work on the car. ( I'm only getting a couple hours per week of wrench time)

[pampadori]

I did some deeper searching and found a thread about the fuel pump wiring and bingo! This picture shows the plug I think I should be looking for based on what you're saying Tony:



This plug has no mate on my chassis of course, since I have removed the engine harness. I wonder why my fuel pump runs whenever the key is on? Must be messed about with up front somewhere. More troubleshooting....

THanks again Tony for pointing me in the right direction!

[boyt911sc]

Shaun,

Test and confirm. The brown/red wire from terminal #85 FP relay socket goes to this white plastic plug or connector as shown in your picture. The reason why the FP is running when IS (ignition switch) @ ON is because terminal #85 is not grounded (open circuit).

Find an appropriate plug and install a separate or stand alone wire harness to the AFS plug. Standing at the rear of the car by the rear bumper:
a). The left side pin (driver side or cyl.#1-2-3) of the AFS switch goes to the white plug.
b). The right side pin (passenger side or cyl.#4-5-6) of the switch goes to D- @ alternator or to any engine ground contact.

A 12-volt test light or continuity tester is what I use for doing such test. If you need new plugs or connectors, contact Dennis Powell (Timmy2). He has all the goodies you would need for the wire and connectors. Keep us posted.

Tony

[pampadori]

THanks Tony. That is basically how i tested it.
I confirmed that when the brn/red wire is grounded in the engine bay, the fuel pump turns off.
When that circuit is open, the FP runs so long as the key is on. Sounds like this is correct.

My new ECU intends to turn the pump on by grounding the FP relay signal wire. So completely opposite of how the factory setup was designed. I'm disappointed by this because I had hoped to just use the same lead up to the factory red relay for the FP and not run all new wires and relay for the FP. Bummer.

[timmy2]

Just install a relay to reverse the fuel pump logic so your (I'm assuming a new EFI) ECU de-energizes the FP relay after the initial 2-3 seconds of prime time. (If your ECU has this feature available. Megasquirt does)
(Relay will open the ground circuit to the original Porsche relay)

[pampadori]

@timmy2 - Great idea! Its simple and solves the issue. It never occurred to me to use a relay to activate ground for a circuit. My mind was only associating them with power. Thanks!