Wiring Diagram Help

[pcivalero]

Hi-
I have an electrical problem in my 1973 T in which none of the interior lights, luggage light, dome light nor clock are working. I have reviewed the wiring diagrams and it appears they are mostly all connected. So, fix the source - fix all the lights. I started with the clock, and pulled it out of the dash and lo and behold it started working. Now - I don't know if it shorts or grounds when I put it back into the dash, but it doesn't STAY working.

Looking at the wiring diagram, I need a little help in understanding a few things. This is Part II diagram.



The clock is 69 which is where the questions are focused around.
1. Looks like clock is directly connected to fuse #1. Black is power, brown is ground. what is the blue and black wire?
2. The clock is number 69, however what I don't understand are the numbers around the clock. For example in the clock there are two numbers 30 and 31 what do those represent.
3. The wires leading to the clock Black (45), Brown (44), Black and Blue (39)...what do these numbers represent?

I can see that in the Part I diagram, the clock then connects to the glove box..hence my thinking solve one problem fix the rest. But how do I trace the wires out of the clock to the glove light? Is that the proper thing to do?

The full wiring diagram is posted here:
Pelican Parts - Porsche 911 Parts Listings & Diagrams

Any help would greatly be appreciated!!!

[ossiblue]

You are corrrect on your assumption that all devices you mentioned are on the same circuit and, logically, fix one--fix them all. You have already identified the power source as fuse#1 and since the clock worked, you are getting power from the fuse. Let's take your questions one at a time:
1. Looks like clock is directly connected to fuse #1. Black is power, brown is ground. what is the blue and black wire? The blue/black wire is the lighting circuit for the instrument, activated by the headlight switch and is in series with all the dash lights.

2. The numbers (30, 31) are the terminal numbers stamped on the rear of the clock which correspond to the ground circuit (30) and the power circuit (31).

3. The other numbers (44, 45, 39) are the current track numbers listed in the diagram.

From what you describe--clock works when removed--I'd suspect a problem with the ground circuit or power circuit, possibly a loose ground connection that is making contact when you move the clock. I believe all the devices you mention share a common ground so that may be your problem. If you had a short, you'd blow a fuse but a loose power circuit wire would shut down all devices.

Also, check that the power wire connected to fuse#1 is clean and tight in the terminal. You should check voltage, with the clock removed at the black wire by using a voltmeter or test light. Wiggle the wire and see if the voltage fluctuates. Do the same with the ground wire.

[356RS]

Lighting problems are usually a bad ground connection. But to answer some of your questions: 1. The blue/black wire is for the backlighting of the clock and also the other gages. 2. The number 30 is the "power in" wire connector. 3. The numbers on the wiring diagram that are labeled on the end of a wire trace, like the "black going nowhere with the number 45", is telling you to look at the rest of the wiring diagram and you will find the other end of that black #45 wire going somewhere else. It just makes it easier to follow than having tons of colored wires to trace on the diagram.

[Grady Clay]

Let me add one piece to L.J.’s good analysis: On the power side of Fuse 1 and Fuse 2 is a jumper on the back side of Fuse Block I (10 terminal). This can corrode where the screw terminals are riveted/swaged in place. Disconnect the batteries. Unscrew the fuse block from the chassis (wires still connected) and inspect the back side.

Best,
Grady

[pcivalero]

Blue, and all thanks...
question, when you say "You should check voltage, with the clock removed at the black wire by using a voltmeter or test light. Wiggle the wire and see if the voltage fluctuates. Do the same with the ground wire."

I did check the power and the voltage goes all over the place, what does this mean? - it was not constant at all...

Also, when you say "From what you describe--clock works when removed--I'd suspect a problem with the ground circuit or power circuit,"

How do I trouble shoot a ground circuit? do i need to trace the brown wire to a potential exposure or do you mean something else?

Thanks again!!

[Grady Clay]

Originally Posted by pcivalero

How do I trouble shoot a ground circuit? do i need to trace the brown wire to a potential exposure or do you mean something else?

Take a voltmeter and measure any voltage at the ground connection on the clock with the (-) of the voltmeter at the battery (-). If the grounds are good, there should be 0.00V. Typical might be 0.10V or less. Additionally, use a headlight bulb from the battery (+) through the bulb and to the ground circuit in question. The bulb should light-up properly. If dim or variable, there is a ground problem. You can then use the voltmeter to find the problem connection.

Best,
Grady

[pcivalero]

next question...i know dumb, but if the black (power) is going to the clock, then where is the out (power) to go to the glove light? how do i follow the wiring from the clock to the next instrument in need of power?

[steely]

It looks like the glove box light, number 24, has the same black wire daisy chained from the clock 69. I found it on the Part I dwg. So your clock should have 2 black wires, one "in" and the other "out".

[ossiblue]

From your voltage test--wild variation in voltage when wiggling the black wire--I'd guess the problem is either a broken wire or loose connection somewhere between the fuse and the clock. If I read the diagram correctly, the clock is the first device in series so if you can find the problem with the feed to the clock, all the other devices should work.

[911pcars]

Some clarification regarding the electrical system. On automotive systems, if there are multiple loads (e.g. motors, light bulbs, accessories) controlled by a circuit wire (fused or not), each of the subsequent loads will be on a branch or parallel circuit. Thus, each branch receives full source voltage supplied by the battery. Only switches, splice joints, harness connectors and fuses are connected in series since they are or should be low resistance connections.

In the example circuit, if the clock works but some of the downstream branch circuits don't (e.g. interior lights), follow the circuit path to ground, probing with a voltmeter to isolate the location of the voltage loss. Per your description, it sounds like an intermittent electrical connection caused by a loose or corroded circuit connector, splice joint or ground. BTW, some loads are grounded directly to the chassis; some have a separate wire connecting to ground (chassis).

Hope this helps,
Sherwood

[pcivalero]

Thanks everyone, very helpful stuff...now another dumb question. I found a couple of old ground wires that have been exposed, OLD and cracking...rather than buying a whole new wiring harness, what can I do to replace the old wiring? Can I cut at the bad areas and replace with new wire? If so..most importantly, where do I find replacement wiring at the correct gauge? Also, would be good to know where to find the (i don't know what to call them) the ends of the wires that connect to the actual components (i.e. lights etc)?

[ossiblue]

Originally Posted by pcivalero

Thanks everyone, very helpful stuff...now another dumb question. I found a couple of old ground wires that have been exposed, OLD and cracking...rather than buying a whole new wiring harness, what can I do to replace the old wiring? Can I cut at the bad areas and replace with new wire? If so..most importantly, where do I find replacement wiring at the correct gauge? Also, would be good to know where to find the (i don't know what to call them) the ends of the wires that connect to the actual components (i.e. lights etc)?

You should be able to find the wire and connectors at any auto parts store or audio/stereo/electronic store and, of course, on-line. Not sure of the wire gauge--I'm thinking either 14 or 16, but others will give the correct gauge. The difficulty you may have is finding the correct color, usually brown for grounds, and I strongly suggest you do not change colors.

The connectors are called "spade" connectors and can be purchased as male/female with crimp-on fasteners and insulation. Again, not sure of the size, 1/4" I believe. Crimp connectors are available for splicing wires together also, though soldering is the preferred method if feasible. All in all, you should be able to splice in new sections without difficulty.

[pete3799]

Cut off the bad ends a take them to your local auto parts store.
They will fix you up with what you need.

[Artfrombama]

I see the Pelican schematics are no longer downloadable. Where can I obtain one?

[Trackrash]

Do a Google search. Then click on images. There is a very good chance that somewhere there is the diagram you want archived somewhere out there. Worked for me.

[ChrisHoover]

I wonder why the Pelican hosted diagrams are gone. Anyone know?

[Trackrash]

Originally Posted by ChrisHoover

I wonder why the Pelican hosted diagrams are gone. Anyone know?

Porsche has lawyers and copyrights.

[76FJ55]

here is the link to a PDF which details the common terminal designations. this can be extremely benificial when trying to understand how components in a system are supposed to work and for troubleshooting.

http://www.bosch-classic.com/media/en/bosch_classic/teile_1/switches/downloads_3/klemmenbezeichnungen.pdf

[76FJ55]

Originally Posted by ossiblue

2. The numbers (30, 31) are the terminal numbers stamped on the rear of the clock which correspond to the ground circuit (30) and the power circuit (31).

good post ossiblue, nice detail, but I believe there needs to be a silght correction in 2. 30 should be Battery hot at all times, and 31 would be the ground side of the clock circuit.

[ChrisHoover]

Originally Posted by Trackrash

Porsche has lawyers and copyrights.

Sad