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drivehard · Joined: 11 Feb 2004 Posts: 50 Location: Phoenix, AZ

I was on my way to work, and my 81 died electrically. I had a faint glow from the alt light. The engine was stumbling a bit. It cut out for a split second then came on full power then all electrical to the fuse box was gone. There is the sound of a circuit breaker that you could hear. So I had my wife tow me home, and with the key on the power came back and went off several times. When I got home I was able to start it up and drive around the block with it dieing once. The alt light does not even have a faint glow now. Is there a circuit breaker or something that would make this happen or do I have a bad ignition switch? Any help would be appreciated.
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1977 924 daily driver
1977 924 project racer - parting out to be sold
1981 924 - New daily driver

Lizard · Posted: Wed Apr 07, 2004 3:16 am Post subject:

well start with the basics, check the voltage with the car running at the battery opt would be 13.6 volts, but no more than about 15 volts, if 12.5 or less you need a new voltage regulator or alt,

at this time I would recommend replacing the ign switch with an audi unit (black)

if you have good voltage and ign switch replaced then time to pull the fusebox out and on the top in the middle is 3 BIG red wires check for voltage to these they are the constance which supply power to the fusebox
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3 928s,

924RACR · Posted: Wed Apr 07, 2004 3:21 am Post subject:

That would definitely make me wonder about the ignition switch, if not the 3-prong connector to the alternator and starter.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Lizard · Posted: Wed Apr 07, 2004 3:36 am Post subject:

drivehard · Joined: 11 Feb 2004 Posts: 50 Location: Phoenix, AZ

why would I have a faint glow from the alt light and now no light at all? I tested immediately at the battery and get 12.76 volts. That is the max I always get from either of my two running 924's. I would like to see in the higher 13 to 14 volt range myself.
_________________
1977 924 daily driver
1977 924 project racer - parting out to be sold
1981 924 - New daily driver

Lizard · Posted: Wed Apr 07, 2004 10:06 am Post subject:

12.76 is abit low, please attach a ground from the alt to the chassis/battery, also make sure the ground from the battery to the chassis is good, as per the light coming on weak this is due to a bad fuse box or BAD GROUNDS, so you may want to replace or clean the ground points up behind the fuse box, also the ground point by each headlight, and the ground point in the back of the car
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3 928s,

John Brown · Joined: 07 Nov 2002 Posts: 903 Location: Leesburg VA

There have been some previous threads, and maybe something in the tech sesssion. Old car stuff. Very common for the wiring to become marginal especially near terminals. I wrestled with something similar on my old 924 until I finally replaced the harness between the alternator and the starter (built a new one).

The wiring is often corroded and or almost broken throught at the alternator, and it usually is under the insulation so it will look fine. To check wiring and grounds use a voltmeter and carefully check voltages not just at the 'point' but differentiate between, say, the terminal post on the alternator and the lug of the wire connector. Use the Alternator case as ground and then go to the ground post up by the battery. You get the idea. Big differences (voltage drops in the wiring sections) indicate bad wiring. Don't forget the ground strap between the alternator and the engine block, it's old.

The problem with the 'charge' light is that it is affected by the bad grounds. For example, if you have bad wiring but the alternator is putting out then the light will be out but no or insufficient charging current can make it into the system. Or, a bad diode in the alternator and it's ouput is weak but the light is only just slightly on. Daytime you won't notice. Also, if the D+ lead is bad then the light will not light, the alternator won't get excitation current either so in short order things will be dead, without a light.
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82

geezergary · Joined: 07 Nov 2002 Posts: 80 Location: sask.ca

Yup - the grounds (-)( or lack of them) will burn you ! Add some ,
paint them brown if you want to keep the faith, but do it !
Don't cost much - and ya gotta start someplace . Bin there - - -

drivehard · Joined: 11 Feb 2004 Posts: 50 Location: Phoenix, AZ

I changed alternators this evening and my voltage is higher, 13.6 volts which is much better than my other alt. I have looked at the ground wires from the battery to the firewall and the engine to the firewall. I added a ground from the engine to firewall and I built a better ground from the alt to the engine. That appears to have helped some. I am dumbfounded as to why I had a total failure but now with no tinkering I have a fully functional electrical system. This morning it had no power to the fuse block at all. Then with some jarring while being towed it came back to life.

I have drove it extensively this evening with the lights on as added load and had no problems at all. I will keep my fingers crossed for tomorrow.
_________________
1977 924 daily driver
1977 924 project racer - parting out to be sold
1981 924 - New daily driver