[ELECTRICAL GURUS HELP PLEASE] Interesting engine fuse panel issue

[rennch]

Hi all,

I've got a 72T with a 79 3.0 engine. I've had some electrical issues the last couple of days, and today I finally limped it home. I'm going to skip some of the details, and just fast forward to the interesting part:

Car would turn over, but would not fire. I thought it was the CD Box. I have a spare Perma-Tune, so I disconnected the three pin connector, and the other wire, and connected them to the spare CD box, leaving the OEM one in place on the fuse/electrical panel on the left side of my 72's engine compartment. Assistant turned the key, and the engine fired. WHEW!! I solved it.

So, I unbolt the OEM (Bosch) CD box, and bolt in the permatune. Button everything back up, and go to fire the motor up. Turns over...won't fire! (huh???)

On a hunch, I had the asst. turn the key while I stood behind the car, peering into the engine compartment. Still nothing. She turned the key and I jiggled the fuse/electrical panel...and the car fired up again. (Hmmmm....) So, I loosened the bolts that bolt the panel to the chassis, and slid it as far back towards the rear of the car as I could. I thought maybe it was shorting out on the fuel pump bracket or something. In any event, the thing fired up and I drove it home to the garage...but I still don't really know what the issue was. Can anyone shed any light?

Also, because the OEM wires have seen better days, does anyone have a source where I can buy OEM-type wires that are similarly color-coded?

Thanks for any insight.

mto

[vol96]

Cant help you solve the problem, but can share that I had the same type problem with completly stock 72e. However, my problem seemed to be in the ground wired on the elect chassis. At least when I disconnected and re-attached them the problem went away. However, after one or two successful start ups the problem returned. So I dis- and re- connected again. Problem went away and did not return. Go figure.

I too would like to find a source for oe color coded wires.

[304065]

Ground wire sandwiched between the electrical console and the body- remove the console and clean everything, bolt it back up and torque it down.

[rennch]

Thanks all...I'll check it out tomorrow.

John...just out of curiousity...where do you keep your car in Hell's Kitchen???

[RoninLB]

I always ran an extra ground to the CD box housing directly

[rennch]

Ronin,

Would you mind describing what you did? Did you drill a hole in it or something?, or just mount it to one of the mounting holes? Then you grounded it to the chassis somewhere?

[RoninLB]

Originally posted by emptyo
Ronin,
Would you mind describing what you did?

on the inside inner engine compartment liner, on the drivers side, about mid way between the engine sheetmetal and upper liner is a ground lug, somewhere behind my CIS fuel filter. John Cramer already stated where it's at. That has to be clean always. Then I ran a 12ga wire from that to the CD box mounting bolt in direct contact with the box. The CD ground, inside the wire plug, should be in concert with the box case.

and sometimes the tach can cause problems.. it's unusual, but I read that it can happen. If I have a crazy CD problem I unplug the tach connector inside the harness that runs along the drivers side to the engine elec pannel.. easy to find because it's a 2 into 1 connector and the tach trigger wire is colored the routine color, I forgot. You'll have to dig for it in the harness.

you should make sure your CD plug wire and box connectors are very clean and making good contact.

You may want to run new wires from the dizzy to the CD for a temporary confirmation of the connections. I don't know much about the SC dizzy CD trigger internals, or how to confirm its operation.

In my experience I have found that the CD is Very sensitive to wiring and a weak coil, that damages the CD permanently ........Ron

[rennch]

All great advice. Thanks Ron.

[filou]

according to your symptoms, i think that you have short to ground on the the way to the distributor rotor. Check cables approching the CD box because they tend by be bend and that where they are more likely to be damaged and crack the vinyl surrounding the wires of electrical cables and create ground to body and that why you are not getting spark and since it high voltage so it only make the process enough easier to happen.
And for that, i will decide between 2 methods of diagnostic if i may explain. The continuity method to see if there a contact or not in a circuit. The resistance method, to test each resistance of the circuit, more time consuming but more accurate.
Visualy observe if the electrical wires of CD are not crack and no contact are made to the ground of car at connections.
If you could do a Simple test, isolate the space between the connectors of CD box and body of car by a piece of thin piece of wood or anything not conductive of electricity enough to stop any spark between that area of body and CD box. And try to start to car.
Keep us in touch.
Truly, Phil.

[rennch]

Today I poked around it a bit. It seems like I have a short somewhere in the 14 pin connector that goes to the front of the car. (nice pickup Phil). I peeled the electrical tape back, and saw no visible issues, but when I jiggle the plug, the car immediately shuts down. So, it's something in there. I suppose I should start with the ground and the power. I'll get cracking on it tomorrow.

Thanks,

mto

[rennch]

Ok, today's update. I'm stumped.

This evening, I replaced all wires from the dist. to the CD box. I had a spare harness in much better shape than my previous one. I also removed the left side electrical panel, disassembled the 14 pin connector that goes from the back of the motor, and cleaned and soldered anything that needed it. Checked all the plugs in the electrical panel and cleaned all the connectors. Put it all back together, fired the car up, and went back and jiggled the electrical panel. Car immediately shut down again. I mean, I'm talking if I move it *1 millimeter*, the car shuts right down. There are NO ground wires pinched between the electrical panel and the chassis. Everything seems to be in fine fettle...but I'm totally stumped. Any more ideas?

Thanks,

mto

[HawgRyder]

Where electrical systems are concerned....cleanliness is more important than godliness!!
If there is any doubt in your mind that the connection is bad....IT IS.
With a problem like yours....the first thing I would do is jump around the plug/socket connection one wire at a time...in other words, make a temporary connection from before the plug to after the plug on each wire in the bundle.
If the actual problem is the connector itself....replace it...or...recrimp the female metal sockets to provide more grip to the male part of the plug (just be careful not to collapse the socket completely).
You can help things along by using a contact cleaner on both sides of the connectors...also..try Stabline 22 or similar to enhance the connections (it's a liquid that helps keep things clean and conductive).
Good luck
Bob

[filou]

Does that situation keep you from driving the car ? Like if you let things the way there are now the car have a great chance of shutting down the road ??? Or you by moving volontarely the wires make the car to shut down ??? i Hope you understand my question ???
Let us know,
Truly, Phil.

[filou]

Actually, i forget to tell you that basically YOU are the problem : Let me explain, you say when and only when YOU jiggle the wires the car shuts down because it is YOU who create a path to the ground by touching cables. YOU are profiding the circuit with a path to the ground. Simply amazing isn't ???? YOU don't get electrocuted because the 911 Porsche system is differant from other systems, just look at the wiring diagram and you'll understand.
Good luck, Phil.

[rennch]

Phil,

Yes...it shuts the car down immediately. For instance, if I go over a speed bump, I feel the car buck and want to shut down...not a good thing if I want to autocross it on Saturday.

Obviously, I need to ground something better...but I'm not sure what it is I need to ground at the moment. The CD box? The fuse/electrical panel itself?

I'm not very good at reading the electrical diagrams, I'm afraid. Besides, it's a 3 liter from a 79 stuffed into a 72, so the wiring is a little different than the diagrams.

I'm an auto-electrical neophyte, so this is all new ground (pun intended...sorry) for me.

mto

[filou]

By starting on one end of fuse panel box, delicately move Only one wire at the time and if you do it in a dim light, you might be able to see the littles sparks trying to make connection for courant. I like i say very slowly and when you get to the problem wire or wires, then disconnect battery and clean everything involving the contacts of courant.
The fuse pole, the screw of the fuse pole, the inner chamber of the hole hosting the end of wire/wires, I mean check for everything. I can look at a connection and tell if you need to clean those contacts or not.
As a matter of fact, i run with the same problem not to long ago. It will happen at idle, car parked and checking everything around the engine right, like just like you, i have moved a slightest bit one the wire and the car just shut down, just like that.
It was a bad contact, along on the fuel pump elctrical supply and when the pump stopped for a slitghest second and that engine would just shut down right there, boooom, just like that !!!!
Put a voltmeter if you can at the juice of fuel pump and watch the voltage drop when you jiggles the wires around. Use alligator clips to connect the voltmeter to fuel pump. That's how i isolate the problem.
The found the area of the wires bundles that give you hard time for connections.
When i say, fuel pump that technique could be used for anything else i guess. You could connect a voltmeter at primary of CD box, to see if by jiggles the wires around you having a drop of voltage ??? Like this, you isolate the problem the side of the problem. This repair is done by feel.
Do not be afraid just be careful that all !!!!
truly, Phil.
Analog meters work best.