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Registered User
Join Date: Sep 2015
Location: Manchester, CT
Posts: 10
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fuse 23 electrical short
I have a 1980 928, 80,000 miles with 5 liter euro spec engine (not original engine).
I do all my own maintenance and have had zero electrical problems since owning the car since 2014 but was driving the other day and the car stereo failed. I checked the fuses and fuse #23 keeps blowing if replaced (shorted). Also, when I drove the car home and turned off the ignition the car continued to run until I switched off the AC. (the AC ignition issue only happened once) I have a short finder & cable tracer but neither have worked to find the short (except that the short finder does show that only fuse #23 has a short). I have checked all interior lights, the radio, radio antenna, clock, accessible wiring, etc. but no luck yet. I also have cleaned all fuses, relays, connectors, grounds, 14-pin connector, post connector near 14-pin, etc. I also pulled the fuse panel and checked all wiring on rear of panel. I have checked all of the reference tools and threads on this site but I am hoping someone has some new ideas after several days of unsuccessful diagnostics. Any ideas or new things to try would be appreciated. I have attached some pics but can take more if needed. Thanks!        
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09-06-2017, 05:05 AM
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You mentioned turning off the ignition switch and the car kept running. Possible defective ignition switch?
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1986 928S 32 valve engine All stock, automatic, 539 Weissgold Metallic, 70K original miles, Hankook Ventus 2 tires. Previously owned: 67 Vette, 427 L88 Stingray, 74 De Tomaso Pantera L. Latest addition: 2000 BMW Z3 Roadster |
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09-06-2017, 06:48 AM
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Registered User
Join Date: Sep 2015
Location: Manchester, CT
Posts: 10
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good idea
thanks, good idea! I will check the ignition switch.
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09-06-2017, 07:23 AM
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Registered
Join Date: Mar 2010
Location: Texas
Posts: 2,135
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Also try removing the defroster relay. There was a reporting of occurrences a while back wherein the engine would keep running when the ignition switch was turned off. Apparently the relay was somehow back-feeding the ignition system to maintain running status. Magic stuff!
It's probably the ignition switch, but it doesn't cost anything to remove the relay.
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John Curry (Drift King) 928OC member Grand Prix White 1994 GTS AT (The GTS) Black 1989 GT (The GT) and Cobalt Blue 1989 S4 AT (The Blue Car) 1986 Euro AT Indishrot 1984 Euro S AT (The Stepson) and Black Metallic 1984 Euro S 5 speed (The Schwartz) |
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09-06-2017, 09:02 AM
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Registered
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Quote:
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1986 928S 32 valve engine All stock, automatic, 539 Weissgold Metallic, 70K original miles, Hankook Ventus 2 tires. Previously owned: 67 Vette, 427 L88 Stingray, 74 De Tomaso Pantera L. Latest addition: 2000 BMW Z3 Roadster |
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09-06-2017, 10:15 AM
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Registered User
Join Date: Sep 2015
Location: Manchester, CT
Posts: 10
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funny that you mention the defroster relay as I had noticed last night while I was taking apart the panel that it was pretty corroded. (all other relays looked good)
I installed a spare & cleaned the connectors. Short still there with or without new relay installed. Thanks anyway. Any tips are greatly appreciated! I will work on the ignition switch tonight. |
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09-06-2017, 11:09 AM
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Petie3rd
Join Date: Jul 2000
Location: Philly PA
Posts: 4,528
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what is the circuit thats protected by fuse 23?
have you check a few different diagrams to verify what it does? I am going to guess its for interior lights if so i would disconnect the battery then remove every interior lamp and inspect it for melting or broken connectors the roof lamps will melt is the lights are left on for more than 15 mins. This is worse with a dark colored car. NOTE with the lamps removed put heat shrink on every connector so if it breaks off it wont short out
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^^^ Stan ^^^ 2019 BMW K1250 GS 2016 HD RK 1988 S4 Auto , Elfenbein Perlglanz, Pearl Gray 1982 5sp Met black and tan sport seats |
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09-06-2017, 01:46 PM
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Registered User
Join Date: Sep 2015
Location: Manchester, CT
Posts: 10
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just tried disconnecting the ignition switch rear connector. Still shorting fuse 23.
MrMerlin I have tried disconnecting all interior lights & glove box light, stereo, power amp, clock, and power antenna but short still there. (I don't think that anything else is connected to that fuse). I also tried disconnecting all colored wire connectors at the bottom of the fuse panel, and all relays. I will keep at it. 
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09-06-2017, 04:21 PM
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Petie3rd
Join Date: Jul 2000
Location: Philly PA
Posts: 4,528
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look under the pod see if you pinched a wire for the dimmer
check the clock and the ashtray for interior lights and the wire feeds being shorted
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^^^ Stan ^^^ 2019 BMW K1250 GS 2016 HD RK 1988 S4 Auto , Elfenbein Perlglanz, Pearl Gray 1982 5sp Met black and tan sport seats |
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09-06-2017, 08:09 PM
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Don't forget the small square red safety lights in the doors. They often corrode right at the light socket.
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George in Indiana 928 Weissach #153 Cayenne S |
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09-06-2017, 08:33 PM
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Registered User
Join Date: Sep 2015
Location: Manchester, CT
Posts: 10
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Thanks everyone for your assistance. I fixed the short!
It finally dawned on me that the short had to be in the electrical panel since I disconnected all the plugs on the bottom and the short was still there. (only three positive and single ground still connected) I took out the panel again and found two corrosion spots on the rear of the panel hidden behind the grey wiring where the connectors are for the front wiring plugs. |
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09-08-2017, 05:09 PM
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# 153
