[astroede]

Fellow 968'ers: Well you might remember I just successfully replaced my water pump and belts. Took the car out for a second longer drive tonight, and quite suddenly there was very strange noises coming from the engine. The engine slowly stopped running as I came to a quick stop, but kept turning over after no more ignition, even with the key off. There was a buzzing noise, and the battery eventually died completely. My initial thought was uh-oh, my new belt job went bad. Mysteriously, I had absolutely no battery power, so I had to call a tow. $100, and back to the drawing board. I'm thinking bent valves and worse. Major disappointment and I felt like crap.



When I got her home, I took off the belt cover, and all was well. Everything looked totally normal. Pulled the plugs, no piston damage, metal, oil, or anything unusual. Turned the engine by hand, and no issues, compression good. Now I started thinking STARTER. I pulled the starter and did a quick bench test...it seemed to operate OK. When I tried to put the starter back in (ignition off but battery connected), as soon as the housing made contact with the engine I got major sparks and the starter kicked. Connected a multimeter and I have 12 volts between the engine housing and the starter housing...with the key out of the ignition. What the *&%(#>?.



I could see no wiring issues at the starter, but clearly something is up in the starter loop. Did I suddenly suffer a short in the starter while driving? The clatter must have been the starter engaging (flywheel appears to be OK). This doesn't seem to be related to my pump repair...just a rotten coincidence?



Any help appreciated. What should I check? I should NOT have 12 volts between the small hot wire and the housing with the key off, right?



Anybody seen this happen?

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[mbardeen]

Check your wires. A couple other people here have had problems with the starter wire insulation degrading and shorting out.

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[tamathumper]

Agreed. The insulation inside the sheath has probably crumbled, and the starter wires coming down from the battery are shorted out. It's not visible with a casual inspection, so pull the outer sheath back.

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[Cloud9...68]

Yep. I had the exact same thing happen to me a few years ago. The starter just randomly started running while the engine was running, slamming against the flywheel teeth and making an awful racket, and it kept doing it even after I pulled the key out of the ignition. I had to sprint into Walmart to buy a crescent wrench so I could disconnect the battery cable to finally get it to stop! I peeled back the sheath from around the starter cables, and found the insulation around the cables to be crumbling, so I cut it back until I found healthy insulation, wrapped the bare wire in electrical tape, and then secured the electrical tape with several zip ties to keep it from unraveling. A klugely fix, perhaps, but it's held for several years. This reminds me that I need to order a new set of power cables from Higher Connections...

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[gbarrier]

Got that T shirt. Looks like when they made the starter cable they laid the small insulated solenoid wire beside the bare battery wire that goes to the starter. Then they insulate the whole thing. There is no insulation between the large wire and the small solenoid wire except the insulation on the small solenoid wire which crumbles and they make contact engaging your starter.



I washed my engine one afternoon only to come back to the shop the following morning to find the car at the other end of the shop. I made a cable of the proper length, placed a smaller wire for the solenoid beside of it (both individually unsulated) and then put heat shrink over both to make a new cable. On the other hand, seeing how long the original lasted, a new OEM one would probably last a long time. Wonder if they still make them the same way.

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[tamathumper]

That's a great point! I have a very expensive CNC machine in front of my car, and I tend to leave the car in gear. I think from now on, I'll be leaving the e-brake on and the car in neutral!

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[flash]

the problem with that is two fold



1. engaging the parking brake while the rotor is hot causes deformation



2. forgetting to release the brake before moving results in snapping the spring that holds the shoes in place, which in turn causes the brake to lock up inside the drum and leaves you stuck unable to move, or at best with a dragging and noisy brake



fixing the wires is the best answer. you have to cut away the sleeve that houses the wires to even see them though.

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[astroede]

Warning! Pictures below are not for the faint of heart.

The 968 experts above were right again, as the pictures prove. It appears this mess all started with a perforated jacket on the harness that could probably stand it the least: the starter/alternator/solenoid cables. As you can see the harness was completely toast.

I highly recommed that everyone who hasn't done so already check out this harness that runs from the starter through the engine compartment to the alternator and above to a connector by the firewall. The heat and age are likely taking a toll on these wires, and the result can be catastrophic in the right situation. A short between these wires will engage the starter and as noted above can move the car if it is in gear. The key does not have to be in the ignition. I highly recommend you check it out. Mine failed while I was driving. The reasoning behind this design stumps me...what were they thinking?

A new harness and rubber boots have been ordered. Removal of the old one was a PITA, but not challenging.

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[MB968]

Guess one advantage of still having my 968 laid up is that I can attend to new things that show yp on the board like the starter wiring shorting out. Looks like mine has been repaired in this area (sheath cut/pulled back and wrapped in tape).



Does the short always occur at the end close to the starter. Since my engine is out, it is easy to do a more extensive repair. If the short sometimes occurs further away from the starter, I could seperate the existing wire in its own sheath (but not looking to do needless work, as I'd like to be driving again soon).

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[astroede]

My opinion: the last 8" close to the starter is vulnerable for at least a couple reasons: 1) it is exposed close to the ground and can be damaged by rocks etc.; 2) when the starter is removed/re-mounted with the cable attached (which I did 4 times during my water pump/belt job), the cable will flex in this area (there is a strain relief higher up) and if already degraded due to age or heat, the wire insulation may crack or crumble, and you won't see it. However, the portion in the engine compartment experiences the engine heat; the outer jacket on mine was quite brittle and the rubber boot at the alternator crumbled in my hands.

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[Swin]

Glad you got it fixed! One more item to add to the inspection list...

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[MB968]

Decided to just strip all the sheating away to see what I had. So it looks like there are three wires in this harness. My engine is on the floor, with no starter, alternator, etc. but I think I'm correct in saying the following about each of the three wires.



One wire in the Y shaped harness runs from the alternator to the starter and connects to the same lug on the starter as the cable that runs directly from the starter to the battery positive side. So, this must be the wire that allows the alternator to recharge the battery.



One wire runs from a 2 pin connector in the engine bay to the alternator. I assume this controls the voltage regulator on the alternator.



The other wire from the 2 pin connector runs to the solenoid on the starter.



Someone previously had taped each of these three wires from one end to the other, and surprisingly they were still in very good shape. Each of the three legs of the Y shaped harness had their own sheathing (with both wires of that leg in the same sheath). Electrical tape over time especially in the presence of gas, oil, etc. can easily come undone. So, just for added safety sake, I'm going to put each individual wire in its on sheathing and bundle each of the three legs of the Y with a lot of zip ties.

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[gbarrier]

At worse case replace the small wires. You can get what you need at advance or autozone. Then put head shrink on the bare larger wire. That tape trick will bite you.

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[astroede]

Update: I was facing a 3 week minimum wait for the Porsche wiring harness to replace my burned up cables, and I have an autocross coming up next week, so I decided to build my own improved version. I bought cables of the correct gauge, heat shring tubing, and lugs at Home Depot. Copying the original cable lengths, I constructed the "Y"-shaped harness. Lugs were crimped and soldered, and heat shrink was placed over the crimp areas. The 2-conductor, white connector that goes by the brake booster was easily disassembled and reterminated with the new wires. No longer is the solenoid wire surrounded by bare copper strands. I installed the new harness this morning, along with some new cable ties and cable clamps, and shazaam I'm back in business. Total cost: about $30 and about 1 hour to assemble the harness.

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[MB968]

What size AWG did you use. I've seen differing conversions from metric (square mm) to AWG.

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[astroede]

MB968,

I chose a larger size when in doubt. I used 4 AWG for the alternator-to-starter cable; 12 AWG for the small solenoid wire; and 16 AWG for the small blue alternator wire. All stranded copper, of course. About 5' of each wire was plenty.

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[JWahlsten]

Nice. I've moved my wiring project to the top of the list for my to dos when I get my new garage in the next couple of weeks. Really, when I get my tools back from the movers...

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[gbarrier]

Great job Astroede. You'll never have a problem with it again.

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[MB968]

When I found that the alternator-to-starter wire that I had was bare, and just wrapped in tape, I decided to replace it. I now have a new #4awg replacement wire. I found some old dies that I had to crimp ends on custom spark plug wires worked well at crimping the new lugs on the #4 wire. I also put another layer of shrink wrap over the top of the other two wires; didn't want to deal with the factory two pin connector and new wires. So, now have a much improved harness that should stand the test of time.



Astrode, when I finally found some good cross references between metric wiring measured in mm squared. I came up with the same #4 awg for the alternator-to-starter wire, and #16 for the alternator voltage regulator. But, the wiring diagram for the '92 968 shows the starter solenoid wire as 4 mm squared. A #12 awg only shows as 3.3 mm squared, and since we can't easlily buy #11, the correct replacement size for the starter solenoid looks to me like it should be a # 10 awg.

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[astroede]

MB968, thanks for the research, very helpful. The red solenoid wire was a close call for me when I was comparing cross sections at Home Depot. But so far, so good. Thanks for the extra info. I'm off to the Chicago Region AutoX at Tire Rack in a few minutes. Happy motoring everyone.

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