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Location: Santa Barbara, CA
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Wiring to Bosch CD unit, 74 911
I've moved a 74 motor to a 73.5. Am trying to sort the wiring. i'm looking at the very tired wires from the CD box's terminals A and C. Both are original I think and were shielded; the shielding was then separately grounded at the D terminal on the CD case and on the motor. I know the CD box case should be grounded at the D terminal, but I'm wondering if the shielding was part of Porsche's attempt to figure out why CIS boxes were blowing all the time, or if I really need it to control ignition noise in the radio. Thanks,
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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10-23-2007, 02:53 PM
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The shielding has nothing to do with RF, it's the ground for the CD box. It came in well before CIS.
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'66 911 #304065 Irischgruen ‘96 993 Carrera 2 Polarsilber '81 R65 Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13) Ex-'88 Carrera (Sold 3/29/02) Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04) Ex-'89 944 Turbo S (Sold 8/21/20) |
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10-23-2007, 03:12 PM
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Thanks John. Good to know I won't lose my radio. But I'm not understanding something. THe box itself is (I think) grounded by wire from the D terminal to the coil and distributor grounds. What is the point of wrapping and shielding the A and C leads (hot to the coil and distributor I believe) and then grounding them?
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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10-23-2007, 03:29 PM
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A is the 460V output to the coil, C is the points contact, B is switched +12v, D is ground.
If you look at the diagram, the leads are separate from the braided ground strap. Do your wires run INSIDE the braid? Can you post a photo of this? It's been a long time since I took mine out of the '71. http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_1973_CIS_Part2.jpg
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'66 911 #304065 Irischgruen ‘96 993 Carrera 2 Polarsilber '81 R65 Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13) Ex-'88 Carrera (Sold 3/29/02) Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04) Ex-'89 944 Turbo S (Sold 8/21/20) |
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10-23-2007, 03:37 PM
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Here's a picture. Not sure it helps. But yes, the shielding which wrapped around the A and C lines has been shredded away at the connector and connected to a terminal to attach to the D post on the CD box. At the other end, the same shielding is again pulled away for attachment to two separate grounds at the coil and the distributor. Everything looks 30+ years old, so likely original. Thanks again,
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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10-23-2007, 04:03 PM
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Hmm, that almost looks like Coax. I cannot say whether it's original.
There is ONE man who can say. . . his name. . . . Warren Hall!
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'66 911 #304065 Irischgruen ‘96 993 Carrera 2 Polarsilber '81 R65 Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13) Ex-'88 Carrera (Sold 3/29/02) Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04) Ex-'89 944 Turbo S (Sold 8/21/20) |
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10-23-2007, 04:42 PM
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Location: Auckland NZ & Newcastle AU
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Hmmm, I think I might have a NOS wiring harness sitting in a box at home, will try to get some pics tonight if it will help...
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Regards, Peter 1992 928 GTS 1993 964 Carrera 2 Coupé |
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10-23-2007, 06:05 PM
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Coax is exactly what it looks like. BUt do any of the rest of you have wiring from the A, B, and C terminals covered with this stuff? Thanks,
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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10-23-2007, 06:46 PM
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That isn't a factory cable at all! It was made by Permatune, and they still sell a similar product, but it looks a bit different, now.
My '73 has the CDI wiring inside a shielding braid, so that is probably why Permatune copied the practice for that outrageously-priced [~ $$300] replacement cable assembly!
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Warren Hall, Jr. 1973 911S Targa ... 'Annie' 1968 340S Barracuda ... 'Rolling Thunder' |
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10-23-2007, 07:34 PM
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Mystery solved. Permatune, not oem. But I still don't know whether I need the shielding. Anybody know? Thanks much,
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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10-23-2007, 07:46 PM
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