Rear Fuse Box - help to identify

[Johnr352]

I’ve posted on my O2 heater and ground wires shorted which in turn shorted the Coil wires. This was a hot mess for those five wires and three more that are part of an unused (on my car) plug receptacle on the engine fuse box. Two questions: 1. Did I kill the Coil itself, when the coil wires shorted? 2. Can anyone identify the receptacle’s use from my pictures? I can’t find it on diagrams but would like to replace the wires anyway and want to know to where in the DME harness they connect.

[pmax]

That's the test port, not connected to anything.

B is to pin 3 Wht
C to gnd Brn
A to 12 BlkWht

[Johnr352]

Pmax, not sure what I’d do without you. Thanks very much. Any thoughts on whether I killed the Coil when the coil wires shorted?

[pmax]

Don't mention it, glad to offer assistance.

See the other thread about the coil http://forums.pelicanparts.com/porsche-911-technical-forum/1016601-3-2-engine-harness-engine-drop-2.html#post12228185

[PeteKz]

John, if you mean the igntion coil, I seriously doubt it. That is made to take 12v to ground anyway. Do you know if it got hot?

[pmax]

Agree with what Pete says, the coil is probably OK unless the heat got to it. How does the plug look ?

[Johnr352]

Originally Posted by pmax

Agree with what Pete says, the coil is probably OK unless the heat got to it. How does the plug look ?

Plug on top of the Coil? Both the coil and the wire looks ok. The green and black wires even look fine up to the coil, it's down line where they meet the O2 heater wires where they met death and merged to one.

[wazzz]

Here are two screen shots of the engine management diagram for your year. Hope this helps you trace what is what and where.

[pmax]

Originally Posted by Johnr352

Plug on top of the Coil? Both the coil and the wire looks ok. The green and black wires even look fine up to the coil, it's down line where they meet the O2 heater wires where they met death and merged to one.

Localized damage is a good sign, keep your fingers crossed !

[Johnr352]

So! Some progress, such that I’m learning much more than I ever wanted to know about my harness - yet I have more to go. A couple of follow ups. I’m working with Peter K at Restoration Design and they will build me the replacement section of my harness. To get that going I had one question (so far). On the DME pin out above and in my (spanking new) Bentley Service manual it lists pin 23 as NCA and is indicated as below. I’m not sure how to read that nor do I know to what it connects. Any info just to rule it out, would be helpful.

I tested a number of connections which was dazzling until I figured out that if the sensor was still plugged in or was designed to be hot all the time, like the idle position switch or ignition switch, it would show continuity at ground. (Negative connection removed at the battery). I split the harness sheath as I had one burned melted wire, the yellow O2 wire to the DME relay, and the other wires in the harness are good/ intact.

Another question, I pulled my coil. A Black Bosch unit. Measuring is across terminals 1 and 15 I’m at 1.56 and 1 and 4 I’m at 5.6k. I’m not positive, but believe those readings are out of spec for the 1 and 15. (.4-.7). Right?

[pmax]

The O2 sensor wire, green DME pin 24, is shielded by a ground shroud connected to pin 23. You have to open the DME harness connector and have a look see. I think NCA means No color available.

I was going to mention this ... hopefully, the heater GND took the brunt of the short and the shroud looks pristine at the DME end, otherwise mught wanna open up the DME and have a look. Pin 23 is grounded internally. Even then, it is just GND so hopefully it didn't get too hot and the components inside are spared of any damage.

[Johnr352]

I did open up the shroud at the DME connector and it is pristine. I have t opened up the DME itself. The heater (yellow) to the DME relay and the heater ground did ABSOLUTELY take the brunt as both wires sacrificed all of their insulation You can see in the second picture the yellow wire and only about 3” of insulation remain.


What do you think of the coil numbers?

[pmax]

Good to hear your lucky streak has continued !

The coil numbers for the primary, maybe check your multimeter settings , clean out the contacts etc, see if you can get it down otherwise your coil is marginally off the spec. Better than 0 for sure.

[wazzz]

I think the coil is good. Primary resistance reading should be in the 1-ohm range. You can't measure it accurately with a standard multimeter but if you clean the contacts, rub your probes against them and subtract the probes resistance, you should be close to spec (0.7 ohm) for this coil. At least for Bosch ref. 0 221 118 322. Secondary is in spec too.

NCA stands for No Color Assigned.

[Johnr352]

Ok! An update and I’ll post some pictures below. Pete K at Restoration Design has been VERY helpful. They made me a replacement harness that includes the O2 sensor wires, the Coil wires, and the idle control test connector and wires. A total of 8 wires (2 grounds). Very nicely done and better was the advice along the way. Also asked for a pigtail with one of the pins from the DME Relay connector. The heater wire was burned almost to the pin and so a new pin with the two wires, one heater and one switched to the front fuse box. I also asked for an alternative to the OEM O2 connector that attaches to the metal bracket. This was where the short began and so I wanted an alternative, (to avoid ever having to think about that connection again) and Pete sent a Deutsch 3 pin. This, a mess of barrel connectors, a good crumpet, heat shrink and galore and the repair begins.

I started with pulling the new harness through from the engine, getting the length right(ish). Easy enough and Pete sent it with plenty of extra wire. I rebuilt the DME Relay connector with the pin, new heat shrink on the bundle and then wrapped it all in the sleeving you can see. Interesting stuff, very tough and easy to wrap around the wires secured with zip ties.

The main splices are in the harness between the engine bay and cabin. I had split the entire harness case here to inspect the wires. This made the splices pretty easy to access. I staggered them using the barrels Pete provided, along with heat shrink. The heat shrink had the glue in as well but I wrapped a few with tape. Less attractive and likely unnecessary. I also wrapped one of the shielded wires with EMI tape. Probably unnecessary but it had been burned a bit. A ton more to do in the engine bay, as I need to sleeve the grounds, install the fuse box, etc. but thought I’d post an update. Of course, I’m a ways off from knowing whether the short hurt the DME, fuel pump, sensors, etc. but will get the wires sorted to then see where I stand.

[Johnr352]

[pmax]

Nice progress.
I assume the black splotches on the green wire isn't damage.

About the O2 wiring, thought this other thread has some good info, that being the low voltage signal susceptible to noise
http://forums.pelicanparts.com/porsche-911-technical-forum/1161024-way-turn-3-2-air-flow-disk.html#post12241291

[PeteKz]

max: I think you are seeing the black stripe on the green wire.

[pmax]

Possibly, I was assuming that green cable is for the O2.