Oops. I think that I just gave myself a new winter project! (electrical)

[jluetjen]

I haven't posted much lately due to work demands, and my 911's been running fine all summer. The clutch is about shot, as well as the crank-shaft seal on the crank-case (PO's fault), and the main shaft seal on the transaxle (my fault). The heater blower hasn't been working this year, so I wanted to get that fixed before I got the car inspected for the year. The project for the winter is to replace the clutch and both seals (and the rest of the usual stuff while I'm in there.)

After diagnosing everything else on the circuit, I bought some relays and swapped out all 3 of the relays behind the dash. In the '69's there seem to be 3 plus the directional relay. The manual wasn't clear which was which, but after swapping them into the horn relay it was clear that they weren't all working.

So Friday morning before work I popped in the new relays, turned on the ignition and the heater blower and Voila! Air was moving. So I shut everything down and started walking into the house feeling good about myself . That's when I noticed the smell of smoke. I turned back and there was a noxious smoke coming out of the ventilation ducts in the dash and the unconnected ventilation port in the back of the trunk. I grabbed one of the nearby fire extinguishers and popped it open into the blower trunk. That didn't seem to be doing any good so then I started to get worried.

After opening the garage doors for some fresh air I went back and disconnected the battery. That finally killed the fire. That was close!

I pulled the blower trunk out and removed the blower motor and left it on the garage floor to postmortem later. First things first, I placed an order with our host for a new blower motor. I finally got around to the postmortem yesterday and after cleaning all of the extinguisher dust off the inside of the blower trunk, I couldn't find any signs of fire. Anyway, I figured I'd hook the battery back up to the car and see if I could figure out what happened. As soon as I got the negative lead close to the battery there was big ZAP across the gap. It suddenly dawned on me that I might have a bigger problem...



Yup. Most of the wiring behind the dash is toast.
(The two green wires are for manual activation of the cold start solenoid.)

I think that I've now got a bigger project for the winter. Anyone else ever have a similar experience? How much of a big deal is it to replace all of the dash wiring?

[hessel1974]

I had a similar thing. The PO in my 911 had the instrument +12v wire connected through to the neagtive on the tank gauge. Smoked like hell and destroyed the instrument wiring and a lot of ground wiring.

If you have access, replacement should not be that hard. i would seen if you can either get the same color leads or find a donor wiring loom which you can use.

[jluetjen]

It looks like it was definitely something in the blower motor circuit. It's kind of hard to see, but here's the center relay of the 3, which is the blower motor relay. It melted down so bad that it melted itself into the socket. I ended up destroying it while trying to pull it out.



It's tied into the rear window defroster (the switch that used for the cold-start solenoid), as well as a bunch of other stuff. Curiously it's not fused. The only thing controlling the current on this and a few other circuits (like the headlights) is the relay. In this case if it welded itself it's not going to be very effective in stopping this sort of thing.

It looks like I'll be ordering a new "Trunk wiring loom" from our host.

[69911e]

John: I have a '70 parts car you can have the wiring from if the 2 years are the same.
Ed

[RWebb]

sorry to hear this John - maybe it was the new relay? or you bumped a wire somehow?

you might want to pull the wiper motor & assy. for access; you can clean them up; grease & install new seals on the stubs

[Wil Ferch]

Another.... "curious, it's not fused" comment about Porsche's idiotic lack of fusing and other electrical faux pas they do over the years on the subject of electrical circuits....quite in contrast to their mechanical design prowess.

[jluetjen]

Originally Posted by 69911e

John: I have a '70 parts car you can have the wiring from if the 2 years are the same.
Ed

Thanks for the offer Ed. The wiring diagrams are different in the shop manual. The part number for the tunnel wiring harness for the 1969 911 is "901 612 003 03". The same harness in a '70 911 is "911 612 001 10". So now the question is -- what's the difference???

[69911e]

John: As I remember they are similar but do have small differences. I am not sure if any differences exist in the area of concern. I have not looked at the wiring diagram in 20 years.......
As I remember I did need to modify the '70 turn signal switch/harness to include an extra wire to be compatible with the '69. I think it had something to do with the hazard circuit, but I am not sure.

[rob911]

stating the obvious (feel free to shoot me down), but do check all the active components before firing up again. Could be some months down the line until the wiring is replaced. The "bad apple" could damage the new wiring.

Different model, but my '84 carrera smoked like crazy from the dash vents. Turned out to be the fresh air blower motor failing/failed (liely a dead short in the motor windings). Disconnected the wiring from it and just rely on airflow.

Good luck with the wiring.

[jluetjen]

Here are a couple of status pictures showing my progress. I started with the far end of the loom and I'm working towards the fuse block. Most of the time this afternoon I spent trying to get the wiper motor out. The secret was to remove the speedo first. Unfortunately being a '69, that means I have to unscrew all of the little knurled nuts from the trunk side, which is not easy given my big hands. After that one thing led to another and now most of the instruments are out.





Next weekend I hope to get the old loom out as far as the fuse block, and get all of the instruments back in with the new loom connections. The last (planned) step will be to transfer the connections from the fuse block one wire at at time (hopefully).

If anyone's got any additional suggestions beyond those mentioned above, I'd be happy to hear them.

[jluetjen]

Well I finally got the old loom out yesterday and got the new loom attached to the fuse block. All that is left are the switches on dash. I'm also going to add some fuse links to the fan motor circuit and the other circuits which do not currently have fuse protection. I'm also going to add a disconnect switch to the battery so that I can isolate the ground lead quickly. Then will come the risky part -- hooking up the battery...

I think that I'm going to try the following strategy to bring up the electrics one circuit at a time. Specifically...

1. Don't install the relays yet, and remove the fuses from the fuse blocks.
2. Check the resistance across the battary leads. Hopefully it will be open, or high resistance.
3. Hook up the positive lead to the battery.
4. Check for voltage on the ground lead prior to connecting it to the battary.
5. If everything is good -- methodically disconnect the battary and then re-add the fuses one fuse at a time and then reconnect the battary after each fuse.
6. Add the relays last.
7. Try to start the car.

Anyone have any suggestions or better ideas?

[jluetjen]

Well progress is being made. I followed the process listed above and...

1. The car didn't go up in flames!
2. The car didn't smoke!!!
3. None of the fuses blew right off the bat!
4. The horn works
5. The interior lights work
6. Nothing else seemed to work.
7. Did I say that nothing went up in flames!!!!

That's all the time that I had today. So I disconnected the battery again and I guess I'll start trouble-shooting each of the individual circuits for voltage next weekend.

[Porboynz]

When doing any major rewiring with smoke/fire potential I reconnect the battery via a spare headlight bulb. I can then test things like the interior lights, indicators, horn etc. If it glows brightly with nothing switched on I know I have a short circuit, but the current is not enough to melt anything and destroy a wiring loom. (You need to disconnect the fuel pump and ignition first of course) It works for me.

[jluetjen]

I'm making progress. I got the loom in and got the car to turn over. But it wouldn't fire. Occasionally I'd get a weak "poof" out the exhaust, but nothing better than that. I checked the battery and it seemed kind of low so I hooked it up to the charger while in the car. It immediately showed 25% charged so I let it go.

After a few hours I checked on it and it was only up to about 75%. Just in case, I separated the negative connection from the battary, after which the charger immediately went up to 100%. Hmmmm.....

I checked the resistance from the positive wire to the negative wire (not connected to the battary) and it was only a few hundred ohms. Curious. So I removed each fuse in turn (both front and back) and none of them had any impact. That suggested to me that it was something ignition or alternator related. After checking the resistance from each of the connections to the power tap in the back left of the car, I localized it to the red and black wires from the MSD6AL box. Thankfully I had a spare (repaired) unit, and when I checked that it was open between the red and the black wires. Ahah!!!!

I don't have time to swap it out today, but hopefully when I put the spare MSD6AL box in, the car should start right up.

Here's hoping!

[Porboynz]

Its always a good idea to remove the negative ground strap when charging a battery, a charger can do unpleasant things to your electrics.

[jluetjen]

Interesting thought Porboynz. I guess my question than is: What happens when you drive your car on the alternator??? How is that different than hooking your battery up to a trickle-charger?

Either way, I had originally charged the battery outside the car, so I think that it's safe to say that the ignition failure was not due to my charging the battery with it hooked up to the car, and more likely a result of the ignition fire back in the fall.

[jluetjen]

Yes!!!!!!