alternator woes.
 

A few weeks ago, my 83 simply stopped charging until it was fully warm under there, and only at very high revs, and sometimes would keep charging at low revs. red OXY (!) light would come on dimly, or bright, and would sometimes flicker in tune with RPM...low rpms.

i installed a bosch rebuild today before work, and on first fire up appeared to have solved the issue. But on the drive home it appeared to suffer some of the same issues...but doesnt need to be warm first. i will charge wonderfully, but now sometimes wont at all, and then yes..OXY(!) light comes on some, or a lot, or not at all now...and not charging. But then right before i parked, worked fine like nothing was wrong.

frustrated...bad rebuild? Any other components i should look at?

Grounds?

Above CE and behind pod grounds...and pod...were cleaned up before Xmas.

Check the blue exciter wire that goes into the back of the alt and trace it up the 14 pin harness. It is most likely highly corroded and causing your charge issues.

Check it's resistance and if it is high, replace the wire.

This car also has a fresh rear PCB put in it right? So the resistor shouldn't be an issue.

Its a brand new Roger PCB in there since October.

Ive had the 14pinopen lately, and it appears in fine shape, no corrosion in the pins. The blue wire looks good at the harness too.

Hmm.....gives me something to trace out when I debug this with a meter and time on the weekend. What should i read from the wife at the CE panel normally?

It's just copper wire without anything inline until the resistor so it should read next to nothing.

The end that gets the most corroded is the end attached to the alternator, they get pretty ugly even when the rest of the harness looks fine.

Exciter circuit
 

What I did on my 83....
https://rennlist.com/forums/928-foru...1983-928s.html

What ever she tells you to read.

Sorry, I just couldn't resist. :)

I hope you get it figured out.

Jeff --

-- Does the charge light come on when you turn the key to "run" prior to engaging the starter? The bulb illuminates because of the difference in potential between the 15 (true when key in "Run" or "Start" positions, and the exciter circuit in the alternator itself. With added resistance or a broken wire, the lamp will be dim or not illuminate at all. If the light stays on after the engine has started, continue...

-- Put a volt meter on the exciter lead at the alternator, reference to ground. With key on and engine not running, you should see at least 6 volts or so there. Much less or nothing means there's extra resistance or a break (respectively...) in the exciter circuit from the dash.


Circuit description for testing:

-- Circuit travels from the 15 circuit through the lamp-or-resistor (in parallel in the cluster), illustrated on wiring diagram X at circuit index 38. Exits from the 15 bus at CE connection H7, to terminal 3R on the cluster, out from connection 1 on the cluster and back to CE connection H8, With key on and engine not running, lift the 14-pin in the engine bay, and test for battery voltage at CE connections H7 and H8. If you don't see that, reseat the cluster connectors and test again. These connections are documented on wiring diagram X, for those playing along at home.

The circuit continues on sheet 1 at circuit index 2, where it exits the CE panel at Z6 and comes right back at Z1 (black), then out again at O8 (blue). With the 14-pin lifted, you should see battery voltage at all of those with key in "run" position but not started. Plug the 14-pin back in, and you should see voltage reduce some to somewhere around 6 volts (depends on alternator and regulator). If you still see battery voltage, there's an open circuit/break in the wire between here and the alternator. Grounding any of these pins with key in "run" and engine not started should illuminate the dash indicator.

The circuit continues to the 14-pin connector to pin 1 (blue) in the bottom half. Again, battery voltage with the connector open and key in "run" position, but engine not started. Grounding any of these pins with key in "run" and engine not started should illuminate the dash indicator. With the 14-pin connected, the voltage should drop to around 6 Volts or so. Hard to test without very carefully removing the connector cover with the connector assembled (else risk the wires popping out of the upper connector body...)

The top half of the 14-pin connector pin 1 (blue) is the exciter wire to the alternator. At the alternator end, with 14-pin connected, you should see the same maybe 6 Volts as you saw at the 14-pin connector pin 1. With the exciter lead lifted from the alternator, you should see battery voltage with key in "run" position but not started. Grounding the open lead should illuminate the dash indicator.

Once everything is reassembled and working correctly, voltage at the exciter terminal on the alternator should read about 6 Volts with the engine not running but key in "run" position. The dash indicator should be illuminated. Once the engine is started, the voltage at the exciter terminal should rise to equal battery voltage, and the dash indicator should go out. If all this happens correctly right up to the part where the exciter voltage comes up and the light goes out, but doesn't make it that last step, your alternator isn't cutting it. (that's why I put this test step up at steps 1 and 2...)


HTH!

Welp, thats my job saturday then :)

Moreinfo...the charge light and OXY light both come on when its notcharging, just not always bRIGHT, sometimes dim, fluttering...and unlikethe last alternator, this one works fine COLD...warms up, issues.

Jeff --

Look for connection and cable resistance issues in that excitation system. With engine off but key in "run" position, the charge light should be glowing solidly. Since you worked on the cluster foil recently, a good first step might be to exercise the edge connectors a few times to make sure the little leaf connections are wiped well by the fingers in the connectors. Some of the other odd symptoms might go away too if one of the connectors isn't fully and squarely fitted to the foil edge.

Its no longer a foil, but a solid PCB, with a proper connector. ;)

So the connection at the cluster backplane, be it foil or PCB, is only a part of the current flow path for the exciter circuit. You'll be able to test the connections through the gauge cluster and connectors by looking downstream, and decide if you need/want to work your way back through that section or forward through the rest of the circuit to the alternator. Each diagnostic testing step is designed to cut the remaining fault options in half. Keep doing that until you have it narrowed down to the only thing it can be. Divide and conquer, or something like that anyway.

For those playing along at home, the diagnostics start with whatever you worked on last. In this case Jeff's list includes the gauge cluster and the wiring connections at the alternator. Testing is at CE pins H7 and H8, looking for voltage with key on, engine not running, and alternator connected/not connected. Last option is easily managed by lifting the 14-pin under the hood to see what changes. Then ground pin 1 of that same 14-pin connection to verify that the lamp comes on bright and solid, and that voltage at H8 is zero. That verifies that the problem is NOT between the ignition switch and the 14 pin connector. If the light isn't on bright, or there's much (more than a very small fraction) voltage at H8, then the connection from H8 to the 14 pin is suspect. You can see how some relatively simple voltmeter testing at just a couple easy CE connector points can narrow the possible-causes list by half.