83' alternator wiring
Thread Starter
AutoX
Joined: Dec 2006
Posts: 13
Likes: 0
From: Tempe, AZ
83' alternator wiring
I have recently aquired a 1983 928 that sat for 6 years. I have been able to get it running again but the alternator was bad so I got a rebuilt & put it in and no juice came out. It turned out that the exciter wire was only putting out about .5 volts. My rebuilder tells me it should need about 6 volts but not a full 12 volts. I jumped the exciter with low voltage and the alternator started charging. I have checked the harness to the main engine electrical connection on the right fender well and the voltage to the connector is only .5 volts. Where does this wire come to the connector from? I have the checked wiring diagrams and they go to another page and I can't find which relay steps the voltage down from 12 volts. The wires in the engine compartment not in very good condition (cracked and peeling insulation) so I plan to jump around the harness if I can find the source.
Thanks in advance for any help,
Tom Errickson
83' 928, 71' Lotus 7 S4, 00' Chevron Super 7, 77' 280Z V8, Van Dieman RF90 F2000,
Thanks in advance for any help,
Tom Errickson
83' 928, 71' Lotus 7 S4, 00' Chevron Super 7, 77' 280Z V8, Van Dieman RF90 F2000,
Thread Starter
AutoX
Joined: Dec 2006
Posts: 13
Likes: 0
From: Tempe, AZ
Yes, I understand for the main heavy charging cable but what about the small (about 12 gauge) wire? It looks like it was blue or maybe green that is in the harness with the main charging cable.
Addict
Rennlist Member
Rennlist Member
Joined: Jan 2003
Posts: 412
Likes: 0
From: Mayne Island, B.C. Canada
In my 79 the exciter wire goes into the dash and is connected to the charge light. When the car is not running power comes from the battery through the charge light to the alternator to excite and light the charge light. Once the the alternator is running it self excites and provides power back through the excitor wire which extinguishes the charge light because there is no longer any potential. E.g. equal volts on each side of light. I belive there is resistor in the dash which reduces the excitor voltage.
Someone like Wally P could do a much better job of explaining this.
Sean
Someone like Wally P could do a much better job of explaining this.
Sean
Addict
Rennlist Member
Rennlist
Site Sponsor
Rennlist Member
Rennlist
Site Sponsor
Joined: Jul 2001
Posts: 11,542
Likes: 4
From: Anaheim California
There is a Porsche Tech bulletin which calls for replacing the resistor on the back of the instrument cluster with a 928 641 981 00 a 68 ohm 5 W resistor which increases the exciter current
Rennlist Member
Joined: Jan 2004
Posts: 12,620
Likes: 8
From: Boulder Creek, CA
If the dash light with the little battery icon is not illuminating then you probably have a bad bulb. If you do not have the added resistor per the tech bulletin that Jim referenced then a burnt charge light bulb will prevent the alternator from charging.
Thread Starter
AutoX
Joined: Dec 2006
Posts: 13
Likes: 0
From: Tempe, AZ
I have not seen a charging light on the dash, only the volt meter. Does an 83' have a light? I might be lucky and it is only a loose bulb. I am at work now and will look closer tonight.
Thanks!
Thanks!
Trending Topics
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
9 Features and Characteristics That Only Porsche People Understand
Verdad Gallardo
I've Written 500 Rennlist Articles: Here's How Porsche Has Changed Along the Way
Joe Kucinski
10 Most Unnecessary Porsches Ever Built (And Why We Love Them)
Verdad Gallardo
Porsche 911 GT3 S/C vs 718 Spyder RS: 10 Categories, One Winner
Joe Kucinski
This Builder Is Turning Heads With Its Slantnose 911 Creation
Verdad Gallardo
Porsche 911 GT3 Artisan Edition Pays Homage to Japanese Culture
Verdad Gallardo
Porsche Reveals Coupe Variant of the Electric Cayenne With a Fresh Look
Verdad Gallardo
10 Porsche Colors That Have More Personality Than Most People
Verdad Gallardo
Guntherwerks' Final Speedster Creation Is the Ultimate Porsche Restomod
Verdad Gallardo
Rennlist Member
Joined: Jan 2004
Posts: 12,620
Likes: 8
From: Boulder Creek, CA
The light should illuminate when you first turn the key to "on", before starting. You can test the circuit by grounding the thin wire that normally connects to the alternator. Play it safe and ground it through a ~5A fuse. If, when you do this after checking/replacing the bulb, the light in the cluster illuminates, then the circuit is good.
Thread Starter
AutoX
Joined: Dec 2006
Posts: 13
Likes: 0
From: Tempe, AZ
Thanks everyone for your insight, problem solved! I finaly got to take the shark more than around the block now that the battery charges. I'm looking forward to putting on a lot more miles.
Tom Errickson
Tom Errickson
Rennlist Member
Joined: Jan 2004
Posts: 12,620
Likes: 8
From: Boulder Creek, CA
It will most likely work, but the single wire hookup will not work properly with the charge light in the dash. The charge light will always be on unless the bulb is burnt or you pull it out. Where did you get the alt?
