Electrical issues.

[Brunoz28]

I recently got a 1979 911SC that may have been owned by Edward Scissor hands. I just spent the last four days trying to sort out electrical issues and came across a slew of cut wires and connections to no where. It was all spurred on by a non-functioning reverse switch which still doesn't work. Hopefully you all can help me sort some of these wires to no where issues.

There was this connection from the fire wall to inside the cabin. Any clues?

[Brunoz28]

There were also these two that were near the brown and white wire that go into the e brake handle. One has current when the ignition is on and the other does not.

[Brunoz28]

And the piece of great resistance, as in its fighting me tooth and nail. The reverse switch. I have read the previous posts, they're very informative. I tried to emulate the steps followed but with no results. Before delving into the project I crossed the wires that go into the switch and the lights did work briefly. Could I have burned something out? After the first flicker it did not work again. I tried running 12V through it to see if it responded and it did not. I pulled the switch and activated it manually while running current through it. the current lit the test light on the other side, indicating it was functioning. When I omitted the cars wires, green and yellow and gray and red, I was able to tell that the switch was working after having replaced the pin and that the pin was indeed the appropriate length. Because when I pushed current straight from a battery to one wire in the switch and activated the reverse gear my test light comes on.

[Brunoz28]

I'm using those massive connectors for now until I get everything to respond accordingly. I cant tell why the current wont go from the switch to the back of the car. Any input would be greatly appreciated. I've cleaned every ground I could reach, I've replace some burned out ground and miscellaneous wires I could find. My next course of action is to bypass the harness and run a power source to the switch from somewhere else and drag that to the reverse lights. I don't want to go that rout since it feels like a tap out. I would love to retain the integrity of the factory wire harness but I'm at my whits end. HELP!

[timmy2]

Remove the 14 pin connector on the back of the fuse panel and check pins 5&6 on the female side of the connector for continuity to the wires going into the switch.
To test the reverse lamps put a jumper across the male pins 5&6 on the fuse panel side of the 14 pin connector and turn the ignition to run, the reverse lamps should be on.
If the second test doesn't work check fuse #6 in the trunk (should have green/yellow wire to it)
If you have continuity in the engine harness wires and the above test works, then the reverse lights should work.
(Plug a nice clean 14 pin connector back in first)
Good luck, and report back.
Did you change the switch or pin?



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[timmy2]

The white plug may be for a radio of some kind.
What color are the wires in question near the hand brake?


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[Dave Colangelo]

Ill offer some general notes about Porsche Electronics that I have discovered over the years.

- Connectors to no where some times are meant as such. It seems that in some cases Porsche wired their cars for all options even if they were not ordered as such (cheaper to make one harness with everything than many different ones is my assumption) or over the years accessories were removed properly (or not) and their connections left as is. Thus sometimes you will find connections that go no where but that is just where they should go.

- If it works and you start to tamper with it, it will break. Some of the hack jobs out there are terrible, if you are diving in be prepared to dive 10x deeper than you think you may need to.


- Always a good edition to any shop...
JEGS Performance Products 10750 JEGS Weatherpack Connectors - Free Shipping on All Orders @ JEGS

- Grounds may not be your issue if you have cleaned them all, start looking for shorts/a burnt bulb/bad components.

- Check your wires, from end to end for continuity of you are curious about why something is not working. Most modern multimeters will have a mode for this.

- Good Luck!

Regards
Dave

[targa80]

Do you have a complete copy of the schematics? You will really need it if you plan to correct the issues with the wiring. They are available from our host under the Parts Catalog window on the left side bar or from the Haynes manual or other tech manuals available. The Heater blower switches are ganged together in parallel near the hand brake each have a yellow wire going to them (this is if you have the two heater lever configuration). The handbrake switch has a brown/yellow stripe wire connected to it's switch. I used the 1982 schematics to ring out all of my wiring on my 1980SC. I found it easier to use than the 1979 SC schematic. The 79SC schematic uses a two separate legends with current track identifiers where as the 82SC schematic has parts identifiers on each part on the schematic. In my case the 82SC schematic was correct for my application. Naturally, I did find where wires were no longer used and I just annotated them on my schematic.

[porwolf]

Originally Posted by targa80

Do you have a complete copy of the schematics? You will really need it if you plan to correct the issues with the wiring. They are available from our host under the Parts Catalog window on the left side bar or from the Haynes manual or other tech manuals available. The Heater blower switches are ganged together in parallel near the hand brake each have a yellow wire going to them (this is if you have the two heater lever configuration). The handbrake switch has a brown/yellow stripe wire connected to it's switch. I used the 1982 schematics to ring out all of my wiring on my 1980SC. I found it easier to use than the 1979 SC schematic. The 79SC schematic uses a two separate legends with current track identifiers where as the 82SC schematic has parts identifiers on each part on the schematic. In my case the 82SC schematic was correct for my application. Naturally, I did find where wires were no longer used and I just annotated them on my schematic.

Pretty good wiring schematics are also part of the Bentley's manual. They go over several pages and address various parts of the wiring separately like all ground connections on one page, etc. Though the schematics are in black and white wire colors are marked in print also. That is what I use.

[Robey5]

Pictures of yellow wires near your hand brake: I am pretty sure that these go to your heat-lever switch.

There is a little contact set that you wire up to, and when you pull the lever, it turns on the squirrel fan (in the "engine room") via a relay.

Speaking from a little experience having worked on a 79; and sorted electrical issues: get a wire diagram. Very helpful.

[timmy2]

The Porsche factory current flow diagram for the '78 that our host has a link to is all you need for your '79.
Once you learn how to read it, it is very accurate and simple. Just remember everything on the bottom is ground...

I have found the Bentley is incorrect in a few places for my '78, mostly at the fuse panel.
Yellow wires are clearly shown on the schematic for the heat lever switches.




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[Brunoz28]

Thank you all for your replies. I will start with the first suggestion and work my way down. I'm keeping my fingers crossed.

[Brunoz28]

Originally Posted by timmy2

Remove the 14 pin connector on the back of the fuse panel and check pins 5&6 on the female side of the connector for continuity to the wires going into the switch.
To test the reverse lamps put a jumper across the male pins 5&6 on the fuse panel side of the 14 pin connector and turn the ignition to run, the reverse lamps should be on.
If the second test doesn't work check fuse #6 in the trunk (should have green/yellow wire to it)
If you have continuity in the engine harness wires and the above test works, then the reverse lights should work.
(Plug a nice clean 14 pin connector back in first)
Good luck, and report back.
Did you change the switch or pin?



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I changed the pin for the reverse switch. I will try the test procedure you outlined if it doesn't work I think I'll be ordering a new switch soon.

[Brunoz28]

Originally Posted by Brunoz28

I changed the pin for the reverse switch. I will try the test procedure you outlined if it doesn't work I think I'll be ordering a new switch soon.

I checked the 14 pin connector as recommended. There was no power on 5 & 6 on the female side; the male side only had power on 5 nothing on 6. I tried to bridge 5 male and 5 female assuming at least one side's reverse lamp would work. It did not.

I checked the fuse for the green and yellow wires there is a thicker one that only comes on when the headlamps are on. The thinner green and yellow wire has power with the ignition on.

[Brunoz28]

Originally Posted by Robey5

Pictures of yellow wires near your hand brake: I am pretty sure that these go to your heat-lever switch.

There is a little contact set that you wire up to, and when you pull the lever, it turns on the squirrel fan (in the "engine room") via a relay.

Speaking from a little experience having worked on a 79; and sorted electrical issues: get a wire diagram. Very helpful.

Thanks Robey5. I've been using various charts actually with varying degrees of success. I'm not sure what's stock and what's been modified so far.

Where on the heat lever did you notice a spot for the yellow wire? I didn't think to look before reassembling it, but nothing stood out when I was combing the area. Thanks for the input Ill go ever the lever more closely soon

[Brunoz28]

Originally Posted by Dave Colangelo

Ill offer some general notes about Porsche Electronics that I have discovered over the years.

- Connectors to no where some times are meant as such. It seems that in some cases Porsche wired their cars for all options even if they were not ordered as such (cheaper to make one harness with everything than many different ones is my assumption) or over the years accessories were removed properly (or not) and their connections left as is. Thus sometimes you will find connections that go no where but that is just where they should go.

- If it works and you start to tamper with it, it will break. Some of the hack jobs out there are terrible, if you are diving in be prepared to dive 10x deeper than you think you may need to.


- Always a good edition to any shop...
JEGS Performance Products 10750 JEGS Weatherpack Connectors - Free Shipping on All Orders @ JEGS

- Grounds may not be your issue if you have cleaned them all, start looking for shorts/a burnt bulb/bad components.

- Check your wires, from end to end for continuity of you are curious about why something is not working. Most modern multimeters will have a mode for this.

- Good Luck!

Regards
Dave

Thanks Dave. I'm starting to get pretty tired of chasing sparks. I might heed your advice and just make it work by any means necessary if I can't resolve it by this weekend. I'd hate to ruin something that's working as I'm trying to move things around to fix this issue.

[timmy2]

Originally Posted by Brunoz28

I checked the 14 pin connector as recommended. There was no power on 5 & 6 on the female side; the male side only had power on 5 nothing on 6. I tried to bridge 5 male and 5 female assuming at least one side's reverse lamp would work. It did not.



I checked the fuse for the green and yellow wires there is a thicker one that only comes on when the headlamps are on. The thinner green and yellow wire has power with the ignition on.

Ok I think you missed the context of the circuitry test.

Put a small jumper from pin 5 to pin 6 of the male connector only. When you turn on the ignition the reverse lamps should light.

Think of it this way, power for the lamps comes from the fuse box on the green yellow wire to pin 5 of the male 14 pin connector. It then goes through the engine harness on pin 5 female 14 pin connector to the switch. When you close the switch the power then goes through the grey/brown wire to pin 6 of the female connector. From there it goes to pin6 of the male connector to both of the reverse lamp filaments and through the lamps to ground.
When the female 14 pin connector is disconnected there is no longer a path for power to reach the lamps.

Let me know if this makes sense. I have a first year electrician apprentice in my shop so explaining wiring and power/voltage flow is something I have to do a lot.




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[Brunoz28]

Originally Posted by timmy2

Ok I think you missed the context of the circuitry test.

Put a small jumper from pin 5 to pin 6 of the male connector only. When you turn on the ignition the reverse lamps should light.

Think of it this way, power for the lamps comes from the fuse box on the green yellow wire to pin 5 of the male 14 pin connector. It then goes through the engine harness on pin 5 female 14 pin connector to the switch. When you close the switch the power then goes through the grey/brown wire to pin 6 of the female connector. From there it goes to pin6 of the male connector to both of the reverse lamp filaments and through the lamps to ground.
When the female 14 pin connector is disconnected there is no longer a path for power to reach the lamps.

Let me know if this makes sense. I have a first year electrician apprentice in my shop so explaining wiring and power/voltage flow is something I have to do a lot.




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Wilco. Ill try that. I'm a medic so I appreciate your patience we could be here a while I hate to introduce new material but, is it normal for slots in the 14 pin to be vacant?

[Brunoz28]

5 to 6 all on the male side worked like a charm. LIGHTS CAME ON! Is there something that could be keeping the current from getting through? Even when the green/yellow is not connected to the switch the test lamp still does not go on. To me this rules out the switch and indicates that something is keeping the current from arriving at the opposite end of the green/yellow wire therefore never getting to the brown/gray or the lights. Is that right? I have no clue where to go from here and I assume my conclusion is probably wrong. What's next?

[Brunoz28]

Originally Posted by timmy2

The white plug may be for a radio of some kind.
What color are the wires in question near the hand brake?


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The wires near the hand brake are yellow. these two I'm holding.