Need electrical help

[jwakil]

I started a thread in the 930 forum but this might be general problem so posting here. My assumption is the general circuit should be similar except I have dual fuel pumps on my 81 930. Anyway, here are the symptoms:

1. fuel pumps don't turn on unless power applied directly to terminal 87 of the fuel pump relay. Applying to pins 30 doesn't turn them on. Starter works and cranks fine regardless. Get spark.
2. Interior lights don't work
3. horn doesn't work
4. Window switches don't work

Things already tried:
1. Switched the fuel pump relays with known good ones, ==didn't help
2. Checked all fuses visually and by twisting ==seemed ok

What could be a common source that would cut interior lights, horn, and fuel pump relay?

[db_cooper]

Alarm system? OEM or aftermarket on the car?

[jwakil]

Originally Posted by db_cooper

Alarm system? OEM or aftermarket on the car?

I don't know of any aftermarket alarm. It probably does have an OEM alarm since there is a key hole in the door jam, but to be honest in the 5 years I've owned I've never used it and don't even know if it is connected, nor do I have the keys for it. Is there a way to bypass it? I thought the alarm just made the horns blow, didn't know it would cut power to other systems.

Forgot to mention, the window switches also don't work.

[donagain1]

Looking at a wiring diagram for an '81 911 (don't know if there's subtle differences in the 930), 25A Fuse #16 is in the path of the red wire feeding term #87A of the Fuel Pump Relay, which jumpers (red also) to term #86 which is the battery side of the relay winding's operate path. Fuse #16 battery feed arrives there from the battery (as opposed to accessory) side of Fuse #11, which gets there via the battery side of @%A Fuse #12, which shares a common bus with a large red/blk wire which leads to term #15 of the Ignition Switch, which gets it's non-fused battery source via the gang of fat red wires that feed term #30 directly from the Battery when the switch is "On".

Essentially it's this... Check the harness that plugs into the back of the Ignition Switch, and whatever bulkhead connectors for being loose. If not loose, then switch the ignition on and test for battery at Fuse #16 on both sides. That's the operate path. Alarm controllers generally interrupt the red lead(s) feeding term #30 of the Ignition Switch, but your car cranks and gets spark so the juice is getting in and out of the switch.

Good luck!

[jwakil]

Originally Posted by donagain1

Looking at a wiring diagram for an '81 911 (don't know if there's subtle differences in the 930), 25A Fuse #16 is in the path of the red wire feeding term #87A of the Fuel Pump Relay, which jumpers (red also) to term #86 which is the battery side of the relay winding's operate path. Fuse #16 battery feed arrives there from the battery (as opposed to accessory) side of Fuse #11, which gets there via the battery side of @%A Fuse #12, which shares a common bus with a large red/blk wire which leads to term #15 of the Ignition Switch, which gets it's non-fused battery source via the gang of fat red wires that feed term #30 directly from the Battery when the switch is "On".

Essentially it's this... Check the harness that plugs into the back of the Ignition Switch, and whatever bulkhead connectors for being loose. If not loose, then switch the ignition on and test for battery at Fuse #16 on both sides. That's the operate path. Alarm controllers generally interrupt the red lead(s) feeding term #30 of the Ignition Switch, but your car cranks and gets spark so the juice is getting in and out of the switch.

Good luck!

Thanks, I will try that. I've had this question for some time but just want to clarify. While this picture of the fuse panel is not exactly for my car (I've noticed some of the relays and fuses are different than what is stamped on the cover of my fuse panel), when we say fuse #16, I assume it is the 16th from the left side of this picture, or 16th from the rear of the car. Is that the generally understood numbering? Reason I ask is that the panel diagrams are numbered 1, 2, 3, 1, 2, 3, 4, 5, 6, ...1, 2, 3.

[jwakil]

Originally Posted by jwakil

Thanks, I will try that. I've had this question for some time but just want to clarify. While this picture of the fuse panel is not exactly for my car (I've noticed some of the relays and fuses are different than what is stamped on the cover of my fuse panel), when we say fuse #16, I assume it is the 16th from the left side of this picture, or 16th from the rear of the car. Is that the generally understood numbering? Reason I ask is that the panel diagrams are numbered 1, 2, 3, 1, 2, 3, 4, 5, 6, ...1, 2, 3.

Never mind the above picture. Just realized that is labeled 1 to 21, however, I have seen others labeled like I described, including what is on my fuse panel cover.

[turbo owner]

Originally Posted by jwakil

I started a thread in the 930 forum but this might be general problem so posting here. My assumption is the general circuit should be similar except I have dual fuel pumps on my 81 930. Anyway, here are the symptoms:

1. fuel pumps don't turn on unless power applied directly to terminal 87 of the fuel pump relay. Applying to pins 30 doesn't turn them on. Starter works and cranks fine regardless. Get spark.
2. Interior lights don't work
3. horn doesn't work
4. Window switches don't work

Things already tried:
1. Switched the fuel pump relays with known good ones, ==didn't help
2. Checked all fuses visually and by twisting ==seemed ok

What could be a common source that would cut interior lights, horn, and fuel pump relay?

Check all of your ground connection, check for power at the lights and horns they could have quit.

[Jonny H]

In the Porsche wiring diagrams for the SC, which is the same period as your Turbo, Fuse 1 is on the RHS nearest to the front of the car. Fuse 21 is on the LHS and fuses 22,23 and 24 are in the engine bay. Physically, the panel is made of three blocks, which have numbers stamped on them. the lid has the same numbers.

[Then, on the Carrera 3.2 diagrams, Porsche refer to the fuses as marked on the fuse blocks and lid. E.g fuse box 1, fuse 1, 2, 3 etc.]

The fuse numbering on the label shown above is incorrect .

It's very confusing if you're not aware of all this! On our replacement panels we stick to how it is marked on the lid.

[jwakil]

Take a look at the voltage I'm getting at each of my fuses. Obviously something wrong. Does anyone know which ones would be direct feed from battery and which would be fed from ignition switch? Ignore the zeros on number four. Number four is connected to 3 so should have same readings.

[donagain1]

Hmmm, yeah... Well, looking at the diagram of the fuse box that you posted, if you start counting from the right side of the box, the 16th one is what's labelled 6 and described as Fuel Pump, so Johnny H's postulate is correct. As the wiring diagram I was looking at last night was not for a turbo, and only showed a single fuel pump relay, and a single fuel pump, it is of doubtful utility. The red wire which feeds the fuse is described on the wiring diagram as a "15", which should be "Switched 12V IGN On", so why exactly you're reading 11V with the key off is a mystery. From what I'm looking at if there were 11V there, that would mean that the Fuel Pump Relay would constantly be operated and THAT can't be right. Sorry I can't be of more help, but for now I must go help Tom Brady get ready for the game today.

[Brian911T]

I was having all kinds of electrical issues and replaced my ground wires at the battery and trans which solved my problems.

[jwakil]

Ignoring number 5 and 6 in the list, do the other readings make sense? Should the window opener fuse for example have power with the key on, or does it only have power when the window switch is activated. Same question for #s 12-21.

[Jonny H]

It's hard to resolve this if you don't speak the same language, e.g. Please use the correct fuse numbers.

For a start, there are brass links (visible and hidden) between the fuses you called 2,3,4 and 5 so it is impossible for the readings to be different unless the link is missing or broken. Either you measured incorrectly or the fuse block is broken or the wrong type.

Time to post a picture of your fuse panel perhaps?

[jwakil]

Well, actually 3 and 4 are connected together, and 5 and 6 are connected to each other on mine. I will post picture but I've done a little bypassing on #4 since I couldn't get the screw out before so I didn't want to confuse people. Also, I confirmed that the reading of 3 and 4 are the same (ignore the zeros on number 4 in my pic, I will correct.

Update. I rejumped the fuel pumps by bringing power to pin 87 of the fuel pumps and was able to get the car started. With the car running, all the electronics function fine. With the car off, everything seems to work but the horn still doesn't work.

[boyt911sc]

Originally Posted by jwakil

I started a thread in the 930 forum but this might be general problem so posting here. My assumption is the general circuit should be similar except I have dual fuel pumps on my 81 930. Anyway, here are the symptoms:

1. fuel pumps don't turn on unless power applied directly to terminal 87 of the fuel pump relay. Applying to pins 30 doesn't turn them on. Starter works and cranks fine regardless. Get spark.
2. Interior lights don't work
3. horn doesn't work
4. Window switches don't work

Things already tried:
1. Switched the fuel pump relays with known good ones, ==didn't help
2. Checked all fuses visually and by twisting ==seemed ok

What could be a common source that would cut interior lights, horn, and fuel pump relay?

jwakil,

There are two (2) fuel pump relays in your 930 plus another relay for the air flow meter and a manifold pressure switch. The last 2 are not used in regular CIS engines except in the turbo's. These additional safety features are covered in Repair Group #2116 & #2529 located in circuit 58 that could prevent the FP's from running. Test and confirm.

Tony

[T77911S]

there is a sticky on the 930 side. look for my posts on TS the fuel system.

remove the wires from each fuse, one fuse at time. clean the ends of the wires with a wire brush and clean the end of the screw. clean the metal tabs on the fuse block. also clean the ends of the fuses. a few twists of the fuses can also work.

check voltage at top and bottom of fuses with neg side on battery ground.

the over boost switch on the IC is a good place to start for no pump run. ground the wire and test pumps.

the 930 FP system is waay different than the 911.

[jwakil]

Ok, I disconnected the wires to fuses 5 & 6 to try to diagnose the low voltage readings. What is strange to me, is that for fuse 5 for example, I have four red wires connect to the bottom of it. But only one of them has power? I would think that at each connection, you either have all powered (supply) or none powered (loads). Why would you have power in one wire and not the others? I'm not sure if my brain is not working or what? Wouldn't this mean that power is being transferred from the power line to the others without going through the fuse?

[T77911S]

Porsche did that.
power for the lights goes thru the light switch and hi beam switch THEN to the fuse.
I don't like that.