'83 911SC, stranded by melting harness in engine bay

[MotoLiam]

Hi Everyone,

I recently drove my '83 911SC ROW for 30 mins in heavy stop and go traffic. Temps remained at the halfway mark on the gauge. I parked the car and had dinner, and 2 hours later tried to start it up. After about ten start attempts, I popped the engine compartment and found this two spade connector and it's wiring completely melted. I tried looking through the Haynes manual I had in the car, and online with the '82 electric diagrams on Pelican, but I can't identify what this connector is for and where the wires go. I haven't been able to strip the wiring harness back far enough - but the connector was on the left side of the engine near the hinge on the driver side.

Here are the pics - can someone please let me know what these wires are for if this has happened to them?

from the front of the vehicle it's 2 wire, red and brn/red, and rear bumper side, brn/red and the red wire splits into 2 wires (maybe I mixed this up, as it was dark when I tried to clip this section out and jump without the damaged connector). My substitute wires also melted when i turned the ignition key - without hitting the starter button.

Thinking it's related to the fuel pump? I'm fairly new to working on Porsches, so thanks in advance. Anything I can do myself will be great, I bought this car to learn more about the breed - looks like this will be one of my first opportunities.

Cheers, stuck in the garage, no start

[pete3799]

Pictures of where in the engine bay it came from would be more helpful.
Check all your fuses. This short may have blown one that is needed to start the car.

[MotoLiam]

Hi Pete,

I'll get pictures up within a couple hours - I checked all the fuses in the front trunk and they are good, and the three fuses visible in the engine bay are also good. I rotated them all around just in case there was some corrosion but that did nothing.

[RD911T]

The fuel pump burned up on my 71 and fried wires back near the area you're talking about. My fuel pump was not fused. Check the wiring at your fuel pump.

[SchnellSchweitz]

Like mentioned above, I believe this is the connector to your fuel pump shut off. The pink wire (if that is pink?) provides a ground to allow your pump to work. With no ground, no pump.

It ties into your CIS.

Of course I could be wrong... since you say it is red/blk. Mine had the exact same connector for my fuel pump shut off, but with a pink wire. Where did you find this connector?

[john walker's workshop]

power plug to the CD ignition unit. brown is a ground wire and they don't like to touch each other.

[don gilbert]

JW is right as usual. Went for a quick look. Looks simular to the early fuel pump connector on mine, but it not.

[SchnellSchweitz]

Yup... I removed my CDI so I no longer see that. JW is correct.

[timmy2]

As John indicated, the red is switched power to the CDI unit. The brown with red stripe wire is part of the ground circuit coming from the pump enable circuit at the air flow switch on the back of the CIS metering plate.

Disconnect your battery and then follow the red and brown/red wires back to where they are still good on the car portion under the rear fuse panel and splice new wires and crimp new connector terminals onto them. Then remove and re-wire your engine harness.

If you want a new engine harness and the materials to repair the burnt wiring on the car built for you this week, PM or e-mail me through the board.
Building SC and Mid Year Engine Harnesses

[MotoLiam]

Hi Everyone,

Sorry it took me so long, but I was working overnight when I posted, having broken down the previous evening. Now that I'm awake; I got a few more pics as requested. These are iphone photos - so not the greatest, and were it not for the huge AC evaporator attached to the deck lid, I would simply have removed it to gain more access/better view (this is still an option depending on how nasty the crispy harness is.

I've got some time this afternoon, so I plan to follow the burnt sections back through the harness and see if I can detect where the fault is (bad wire insulation or bad ground come to mind).

I will solder in fresh wires (have a butane soldering iron), but first it's looking like I'll have to remove the silver aluminum tray that has some relays and fuses on it so I can get to the harness beneath. I have already disconnected the battery and it is being charged at the moment.

If JW is correct, can anyone comment on whether or not something like this is "typical" for a 30 year old 911, because I've spent years rebuilding/restoring classic japanese cars and I've yet to fry a bunch of wires without some kind of user mistake. I want to prevent any future breakdowns and have the 911sc available for daily usage, but not at the risk of being stuck somewhere. I must admit, I'm somewhat shocked that I could arc weld this much wire together without blowing a fuse first . . . JW - can an amperage surge like this fry the CDI?

Here are the pics, I'll update more when I get deeper into it. Note the wires are coming from a section that has a large black rubber protected plug on it - guessing this is the CDI connector?

Thank you all for your help thus far!

[timmy2]

CDI plug has the red wire in it. The brown red goes to the safety switch. Porsche also fuses everything downstream of the switch to the load, not conventional method as per us or Japanese cars. It will melt the switch before blowing a fuse! Follow the logic in the schematics and you will see unfused power everywhere.
The 12v short was before reaching the CDI so it probably is fine. The red wire is power in to the CDI.
Good luck,

[MotoLiam]

Well, I managed to unwrap and check part of the harness this afternoon and here's a drawing of what's going on - but no answers yet as to why or where the real problem is.

From the CDI plug, the thicker red wire that leads back into the main engine wiring harness that runs along the left side of the car up towards the interior is heating up and melting as soon as I turn the ignition key to the first stop, ON position. The second red wire leads from the CDI plug back to the main wiring harness but this one heads back towards the rear bumper into a plug under the aluminum plate I think. That Red wire does not heat up the same as the larger one, despite being spliced directly to it.

I tried running the BrownRed wire directly to ground on the engine in an attempt to bypass any grounding issues within the harness itself, but this had no effect.

I am thinking that either the CDI has something wrong internally, or one of the large brown wires coming from the CDI are not properly grounding somewhere. The ground wires from the CDI are thick Brown and thick Brown/White. The diagrams I have in my Haynes Manual (same as the online ones on Pelican) don't show me enough to "figure it out on paper", so I'll have to remove the CDI, and the aluminum plate underneath that is bolted to the engine bay left side wall. The wiring is a bit messy here because of an aftermarket installed AC, and the relays and such are on the aluminum plate making it harder to get underneath it.

The CDI wiring goes over to the engine, with 2 wires heading into the coil (which I tightened, they were a little bit loose on the terminals), and the rest of them I can't tell because they run under the smog pump.

Timmy2, since I jumped the Brown/Red wire directly to ground (not to the safety switch or the pump enable circuit at the air flow switch on the back of the CIS metering plate), any other thoughts concerning which ground wire I should be chasing?

JW - any other advice I can work off of later tonight after dinner?

I appreciate it all everyone - I checked around for a Bentley SC manual, but no one I know has one, and Parts Heaven in Hayward was out of stock when I called on Saturday. Anyone in Walnut Creek/Concord area have one I can borrow for a few days??

Thanks everyone, all the advice from Pelican makes it evident that this is an enthusiast forum - which is just what I was looking for!

[timmy2]

I'm not sure there should be 2 reds at the melted connector, most cars only have one. Perhaps a PO wired something in for switched power at that location and has left you with a mess!
Is the second red wire leading to the front of the car crimped into the male spade connector or attached some other way? Cut it off going to front of car, repair the remaining piece that is switched power to energize the CDI , ground the brown red wire and see If it will run.

[MotoLiam]

Originally Posted by timmy2

I'm not sure there should be 2 reds at the melted connector, most cars only have one. Perhaps a PO wired something in for switched power at that location and has left you with a mess!
Is the second red wire leading to the front of the car crimped into the male spade connector or attached some other way? Cut it off going to front of car, repair the remaining piece that is switched power to energize the CDI , ground the brown red wire and see If it will run.

Thanks for the response Timmy2 - I checked the red wire going to the front of the car - it is insulation damaged up to the fusebox, #11. I'm not sure what the second red wire, that runs under the aluminum panel goes to.

Then I started looking at the CDI plug. With the battery disconnected and the Permatune CDI disconnected, I checked the #1 pin ground wire for continuity to the chassis (actually, I checked it to my AC compressor body). With the plug disconnected, I had no continuity to ground.



Permatune Plug Disconnected, no Battery:
1 - Brn, and Brn/wht, No Continuity to ground
2 - Blk/Vi, No Continuity to ground (didn't expect it to)
3 - Split green wire, No Continuity to ground
4 - White, No Continuity to ground
5 - Could not check voltage without frying the wire, but No Continuity to ground
6 - Split green wire, No Continuity to ground

Permatune Plug Connected, no Battery:
1 - Brn, and Brn/wht, CONTINUITY to ground, 0 ohms resistance!
2 - Blk/Vi, No Continuity to ground (didn't expect it to)
3 - Split green wire, No Continuity to ground
4 - White, No Continuity to ground
5 - Could not check voltage without frying the wire, but No Continuity to ground
6 - Split green wire, No Continuity to ground

I contacted the previous owner, who had just had the car serviced two days he sold it and installed the Permatune CDI and brown coil at the same time. That was a few weeks ago. I then reached out directly to Permatune, who gave me some advice on checking grounds, and then when I told them that I had continuity to ground on the brown #1 pin while it was connected and no continuity to ground when the CDI plug was disconnected, Permatune said their box was fried and that I would need a new one.

So - it looks like I'll need to fix my wiring issues, and then replace the Permatune CDI, go to OEM, or go to MSD. The previous owner said that he had an MSD installed earlier in the car's life, but that a few weeks ago his shop recommended that he go to Permatune in order for the car to run properly. 2 days later I bought the car.

I am going to take the car back to the shop that installed the Permatune on 5/22 and see what can be done.

Thanks for all your help and advice everyone. I may end up going to MSD and wiring direct to the starter +, running my own wires to the coil, etc. I've got the 101 projects book, so that's might be a good start. We'll see. Thanks!