Looking for help troubleshooting electrical problem

[keitho64]

Sorry for the long post but I am experiencing an electrical problem. I am trying to revive a 1969 911T from a long rest. The car was purchased in pieces and is now all together. I know I have a circuit that is shorted to ground but I need help in identifying this circuit.

Off the ignition switch there are two red wires connected together going to pin 15 on the switch. This connection is fed power when the ignition is in the run position. I have traced the short to this circuit. If I ohm this wire to ground I have a perfect connection. Hence my reasoning for the short.

It seems this circuit feeds the engine compartment so I disconnected all of the connections from the harness in the engine compartment, removed all 12-volt connections form the panel in the compartment, disconnected all wires from the starter. I think I have every wire removed and taped to avoid shorting.

Now when I ohm the suspect wire from pin 15 on the ignition I still have a perfect connection to ground. I am assuming this wire must feed the accessories in the car/dash as well.

My service manual does not seem to show this connection on the ignition as being two wires.

Does anyone know what these two wires feed? I am stumped with the problem, which should be easy to find. I am stopping for the evening and thought I would pose this question to those in the know.

Thanks for any help you can shed. I know this is hard to explain but I have tested the ignition switch and know it is good. It is just this one wire, pin 15 fro ignition, that is shorted and I am trying to trace.

Thanks

[feelyx]

Try removing the ign. switch from the circuit and see if you still have a short.

Tim in Sac

[pwd72s]

Here's a link to electrical diagrams, posted on this site. Hope it can help. http://www.pelicanparts.com/911/911_Parts/911_electrical_diagrams.htm

[keitho64]

All,

My ignition switch is removed at this time so it is not a problem. I am jumping the 12 volt feed that comes to the ignition switch directly to the 2 wire connection that used to plug into connection 15 on the ignition switch and the fues still blows. So my reasioning is the switch is good since I removed it from the circuit and the problem still persists.

I looked at, and printed off, the electrical diagrams. The problem is my car has a 12 connection fuse block and another 4 connection fuse block. So I am not sure if the diagram I have is correct. My car is a 1969 911T chassis but the wiring does not look like anything in the books.

Any other suggestions?

Thanks

[911pcars]

Keitho64,
My wiring diagram shows, like yours, only a single wire connected to terminal 15 on the ignition switch. This red w/green(?) trace goes to the number 7 fuse position which is a junction which also supplies fused current to the rear window heater switch (item 35 on diagram) and the fan motor (item 81). From the junction at fuse 7, the circuit continues to the fuel pump (item 8). On the 69 "Ts", the fuel pump (Hardi) is in the engine compartment on the left wall near the gas hood support strut. Disconnect this fuel pump wire and remove No. 7 fuse (to isolate the circuit) and see if there is still continuity to ground. If so, there is a short in the wire harness. Remove the junction wires at fuse 7 and test again. The objective is to find the section causing the malfunction, then gradually isolate the wire causing the malfunction.

Not sure what the second wire at ignition switch term. 15 is for. Perhaps the PO transferred it from another switch terminal or added a circuit for some reason. Find out what red wire is blowing the fuse, then disconnect it from the switch. Repair or leave the fuel pump wire connected to the switch. Later on, figure out what else isn't working due to the disconnected wire.

The Porsche wiring diagrams (the early ones at least) are a pain in the ass. Trying to trace a circuit is a lesson in sado-masochism. Porsche tried to save repair manual pages by cramming everything onto two pages. Either that or they expected all techs to be master mechanics. Electrical troubleshooting is a continuing problem for service personnel. Manufacturers now realize this and in current repair manuals (can't speak for Porsche), the thickest part of the book is the electrical/troubleshooting section.

Hope this helps,
Sherwood Lee
http://members.rennlist.org/911pcars

[pwd72s]

Sherwood, Keith? I'm puzzled. But, that's not unusual I note TWO wiring diagrams in my old workshop manual. Page SL33 has, shows a single solid red wire leading from post 15 of the ignition switch. The other wiring diagram, on page SL35, shows the red with (dark green or blue, maybe black?) trace that Sherwood mentions. I also have a 2 page diagram, but it is 1971 model year specific.
Anyway...Keith? Color copy of both SL33 and SL35 are on their way to you tomorrow, to the snail mail address you private messaged. If I had to hazard a guess, I'd guess that SL33 is for the '69 model year...but it's only a guess.

[keitho64]

Sherwood, Paul, & all

Thanks for all the input (and diagrams). As near as I can tell the solid red wire feed off pin 15 on the ignition goes to the powering the engine compartment. The second red wire (which is solid red as well) appears to feed the dash. I am in the process of tracing this now. It sure looks like factory wiring but I am not sure.

I am getting ready to go in the garage and trace some more. This is one job that requires a LOT of PATIENCE.

Stay tuned for further developments and hopefully the answer in the next week. I doubt I will find the short any time soon.

I would like to thank everyone for their assistance. Troubleshooting electrical problems is bad enough let alone via email.

Thanks!

[Roland Kunz]

Hello

Maybe built in 69 but still a 68 MY ?

You will find the vin showing 118....

Fuse boxes up front behind the driverside battery or on the trunkfloor beside steering colum ?

Input for the switches are Kl 30 the switch then sources the Kl 15 wires.

One is to the light switch or hazard flasher and the other feeds the fuseblock and the instruments.

However the colorcode for Kl 15 is red/black while red is always direct battery ( Kl 30 )

Grüsse

[pwd72s]

Keith..just read in the paper that the Post Office is closed today.
D-OH! on my part. But do plan on getting the copies made, and they will go out of here tomorrow...You may be relatively new to the board..Roland knows his stuff! And how!

[keitho64]

Well I spent the past two days tracing wires and here is what I have found. The two red wires from the ignition switch that are tied to pin 15 provide 12 volts to the dash gauges and to junction 6 on the fuse block. The end of my ignition switch has a 6 pin plug that connects to the firewall. When I stripped back the tape from the rats nest of wires these two red wires change to one red wire and one Blue/Yellow. In my car the red wire feeds back to the engine compartment and powers the fuel pump and Ignition amplifier. When I disconnected the wire from the fuse block that goes to the engine compartment the short to ground went away at the ignition switch. AHA! I have narrowed down the problem, now I must trace back to the engine compartment. I attached on lead of the ohm meter to this wire and headed back to the engine compartment to find where this wire makes it way into the engine.

This wire feeds the panel on the driver side quarter panel. From what I can tell there is a 2 junction fuse block, two small round relays, one rectangular relay (I think for the rear defroster), fuel pump and Perma-Tune box.

I have a Bendix fuel pump on my car that has one wire on it. If I ohm this wire to ground I have a connection. I think my fuel pump is bad! I assume this wire should be a 12-volt source to the pump. However, even with the fuel pump disconnected I was blowing fuses. Next I found a purple wire from the Perma-Tune box (I assume ignition amplifier), which was connected to a “T” that had the fuel pump connected as well. When I ohmed the purple wire to the ground it had a connection as well. When I removed this wire from the 12-volt source I no longer blow any fuses.

So it appears as if the fuel pump is bad. On the Perma-Tune box I do not know what this purple wire is for. Does anyone know what the purple wire on the perma-tune is for? I have a feeling this is bad as well.

Thanks for all the help. I now feel like I have been baptized in the world of 911 electrical systems.


Thanks for everyone’s help!

[keitho64]

OK, Here is the latest. Paul was kind enough to send me a drawing of the 71 schematic and it was the closest to what my 69 is. (I won't even try to explain that) Anyway, there was a yellow wire in the engine compartment coming from the front of the car connected to another yellow wire on the fuse block. This appeared to be factory wiring. In reality the yellow wire from the front was a ground and this was connected to a 12-volt source. Hence this is where the short was.

I rewired the engine as per the 71 drawing from Paul (Did I say THANKS Paul!) and that resolved the short. Once the wiring was corrected the car started after a LONG sleep. Now with the engine running I am going to complete all of the little details to get the car on the road. If things continue to progress at this rate I will have the car on the road within two-three weeks.

Thanks for all of the assistance; I now have a running engine in the project. All that is left is to connect the clutch linkage, throttle linkage, headlight & taillight wiring and then it is fine tuning time.

[RoninLB]

Good - Good - Good

[pwd72s]

Glad we could help.