Flormat

For those of you familiar with my previous alternator not charging post here is the update.
Ok, my exciter resistor arrived yesterday and I installed in on the back of the clusters volt meter. Fired the car up and still the battery showed only 11 volts with car running. Higher engine speeds to not increase the charge.
I suspected perhaps a bad ground from the negative terminal of the alternator so I removed the negative wire from the alternator. Fired the car up and I got the exact same readings, 11 volts. I assume this means I have a bad ground for the altenator, what do you guys think? And if that is the case could I simply ground it to the frame or block someplace near the alternator or must I use the same ground and track down the problem. Thanks for any help on this.

Dennis Wilson

Is the 11 volt reading at the jumper post or are you reading the volt meter at the instrument panel? The instrument panel meter is often incorrect. If the reading is from the jumper post, try cleaning all of the connections there, at the starter, at the battery and the battery ground.

Dennis

Flormat

11 volt reading is at the post and when I hook the multi-meter directly to the alternator. All connections are VERY clean.

WallyP

Jim Morehouse had the same problem not too long ago, and came up with a neat test rig and procedure. Here is what Jim had to say.

I had to test my alternator recently and thought what I picked up from the alternator
rebuild guy might be of some use to others. Thanks to Wally Plumley who pointed out that:
-This test will not detect intermittents due to vibration/temperature
-This tests the alternator/voltage regulator combo as a unit. Past posts have pointed out
failures/failure to replace old regulator on re-builds. If you're going to a local rebuilder,
make sure they test the voltage regulator, either seperately or on the rebuilt alternator
before you take it.

Background:
I had a problem where my pod voltmeter read (accurately) about 11V or so and the
discharge light came on. The OXS light also came on, but the consensus opinion was that
this was probably an anomaly due to the low voltage condition and that the alternator was
the likely culprit. I took the alternator off the car, took it to a local rebuild shop and it
tested ok (regulator also). The guy gave me some advice on how to test it on the car that
I'd like to pass along (and he didn't charge me anything. He just wanted my business in
the future. You bet!).
I cleaned all the battery and alternator connections, re-installed the alternator, and then
went through the following tests. Everything worked fine, voltmeter around 13+ and
discharge light OFF, so I either had a bad/dirty connection or (shudder) I have something
loose that is OK for now but may fail again in the future.

Alternator operation:
On my '82 5 spd, the Paris Rhone alternator has two terminals, a "-"
that connects the exciter coil to the battery via the Pod discharge light (which has a
parallel 68 ohm resistor), and a "+" that has the heavy red cable on it that goes to the
battery/starter and supplies the charging current.
When the car is turned on, current flows through the discharge light and resistor to the
exciter coil which causes the alternator to juice up to ~ 14V and charge the
battery/circuits. When the alternator is functioning, this "-" terminal voltage rises to 14V
and, since the voltage is the same on both sides of the discharge light, no current flows
and the light is OFF.

TESTING:
Equipment:
- A voltmeter (optional but useful)
(a) Test jig-easy to make up.
-Buy a 'side marker' light socket at your local auto place, a simple socket w 2 leads, and a
compatible bulb of 3 W or so...not too critical. A 3W bulb is roughly equivalent to 60 ohms
at 13.5 Volts
-Two clip leads and wire...solder/crimp the clip leads or alligator clips to the bulb socket
wires. About 1 foot in length is more than enough
(b) Two wires with connectors (circular rings that will fit on alternator terminals or you can
use a good alligator clip to grab the "+" terminal...about 3' for each is plenty. Rings/clip on
one end and I used alligator clips on the other ends
(c) One jumper wire with a clip lead/alligator clip on each end, 1 ft is enough

PROCEDURE:
-Prior to removing the alternator or connecting any other wires to it,
Disconnect the battery by removing the negative terminal connection
(Wing nut on mine)

-I removed the alternator and its shroud so I could get at the terminals

-Attach one wire [(b) above] to the "-" terminal and the other wire to the "+" terminal

-Remount alternator w/o shroud leaving OFF the wire that normally attached to the "-", I
put some tape around its connector just so it didn't inadvertently touch the other wires.
Re-attach the heavier, red, cable to the "+".

-Route the wires away from the engine toward the rear to keep them out of harm's way and
attach the other end’s clips to a small piece of cardboard/wood (not touching each other).
This keeps them from shorting together

-Re-connect the battery negative terminal

-With the car off, I measured to make sure that battery voltage was present on the "+"
terminal. (Measured at the clip lead to the + terminal). If not, you most likely have an
open somewhere between the red cable and the battery (I assume there's a fusible link
between the alternator and battery but didn't have to check this so if you have this
problem you'll need to check the wiring diagrams in the manual)

-Start the car and attach one end of the test jig (a) to the wire you connected to the "-"
terminal. Briefly touch the other end of the test jig to the wire you connected to the "+"
terminal. The light in the test jig should light briefly and then go out indicating that
alternator is working and the exciter terminal (-) has come up to alternator output voltage.
If it stays on, you likely have a problem w the alternator (alternator is not functioning and
the jig light is getting current from battery to ground through a defective exciter coil). Also,
double check to make sure your clip on the "-" terminal didn't short to ground somehow.
If it doesn't come on at all, you again may have an alternator problem (open in the
alternator exciter) or a bad clip lead connection. Again, you should double-check it. With
the car running, you can measure the alternator output w your meter by connecting to the
clip lead going to the "+" terminal, and ground or the jumper connection under the hood.
Should be around 14 volts. (At least greater than 12.6!)

-At this point, you may want to re-try the test with a different battery just to be sure your
battery isn't bad. If the battery is OK then it's time to replace the alternator.

Once you know the alternator works:
To check that you have a good connection and components from the pod (discharge light
and resistor) to the exciter coil:
-Turn the car off
-Remove the test jig
-Take one clip lead of the wire jumper (c) and connect it to the thin wire that normally
goes to the "-" terminal (this is the one you left off earlier and taped).
-Connect the other end of the jumper (c) to the wire you connected to the "-" terminal.
(This restores the
"Normal" connection from the pod light/resistor to the alternator "-" terminal)
-Start Car
-Measure the voltage on the + terminal by connecting one end of meter to the wire you
connected there and the other to ground. If its greater than 13v or so the alternator is
running OK and your connection is OK.

-If the alternator is not functioning you have a bad connection from the pod AND:
1.IF the discharge light is OFF, you either have an open in the wire run from the pod or the
resistor/discharge light are bad (a double fault?..Not very likely)
2.IF the discharge light is ON, you may have a short to ground from the pod

TO CHECK THE WIRE from the pod to the alternator:
-Disconnect the jumper (c) from the wire on the "-" terminal. Make sure it is not touching
anything (tape it if you have to)
-If the discharge light is on, you've got a short to ground between the pod and the
alternator exciter wire.

Jim Morehouse
jim928@ptd.net
Allentown, PA
'82 928


Hope that this helps.

Flormat

I'll test it tomorrow. After reading Wally's post I realized something... When I was installing the cluster today I noticed a black wire coming from the plug connecter on the volt meter side of the cluster. That black wire was broken. There are a few other broken wires under the dash from the PO's previous stereo intallations so I didn't think too much of it. But I'm willing to bet this black wire is the culprit. I'll let you know what I find out. Thanks everyone.

Flormat

I tested the broken wire I suspected but it was nothing.
I performed the alternator test today. Assuming I did it right I am still stumped. When I hooked the light up to the alternator and started the engine the light stayed continuously lit and never went out which according to the instructions means "alternator is not functioning and the jig light is getting current from battery to ground through a defective exciter coil"
I then checked to see if I have a good connection from the pod (discharge light and resistor) to the exciter coil. When I performed these tests the discharge light did not come on. According to the instruction this indicates I have either have an open in the wire run from the pod or the resistor/discharge light are bad. The resistor is brand new from 928 SP so that's not it. Anyone know were the wire between the pod and alt. is routed? And where is this exciter coil? Is is possible to run my own wire from the negative terminal of alternator to one of the two wires to the resistor on the back of the volt meter?
Thanks for all your help on this.

WallyP

"I performed the alternator test today. Assuming I did it right I am still stumped. When I hooked the light up to the alternator and started the engine the light stayed continuously lit and never went out which according to the instructions means "alternator is not functioning and the jig light is getting current from battery to ground through a defective exciter coil"

Sounds as if you have found the problem.

The alternator must have an exciter current to start generating. This exciter current is used to create the mgnetic field inside the alternator.

As the write-up from Jim said, if the light stays on, the alternator isn't generating. It's bad.

Flormat

Ok thanks Wally. But shouldn't the discharge light be lit then?

jim morehouse

Flormat...let's see if this helps out any.

The 'excitor' coil is inside the alternator and is connected to gnd internally and to the '-' term of the alternator on the other end. The way the alternator works is that current is supplied to this '-' terminal which 'activates' the alternator and you see +13.5 or so volts on the alternator output. This current normally flows from the +battery connection in the pod, thru the discharge light and resistor in the pod, into the - terminal on the alternator, and then thru the excitor coil inside the alternator to ground. When the alternator is going, this - terminal rises to equal the battery/alt output voltage and thus there is no voltage difference between it and the battery ...therefore no voltage difference across the pod discharge light/R and so no current flow/light. (or, for the test jig, the light goes off).

If
-your connections are good;

-you disconnected the wire which normally goes to the "-" terminal (and then to the pod);

-and you did the test correctly..
That is: 1. disconnect the "pod" wire from the "-" termianl 2. with the 'normal' wires on the alternator + terminal, start the car 3. connect the side marker test fixture between the alt + terminal and the alt - terminal..this supplies the excitor current mentioned above to 'start' the alternator and once the alternator starts, the "-" terminal will have the same voltage as the "+" and the marker light will go out. You can check the alternator function by measuring the voltage at the alternator + terminal...it should be greater than ~13v if the alternator is ok. If the light stays on, then the alternator isn't starting. Since you've eliminated the pod circuit from this test, then the alternator isn't functioning properly (this assumes you've got a good battery connection to the alternator + terminal but sounds like you have since the light stays on)

" Is is possible to run my own wire from the negative terminal of alternator to one of the two wires to the resistor on the back of the volt meter? ".......yes, you could but I think you need to first clear the alternator malfunction. I confess that I'm a bit surprised that your testing also seems to indicate a fault w the pod wiring...seems to be a double fault and this is improbable but not impossible.

This will make no sense but when I had similar alternator problems, one of the things I did was do a thorough cleaning of my ground and positive connections at the battery and wing bolt. That 'fixed' my discharge light on problem.I did the alternator testing after doing this cleaning.

You might want to remove the alternator and find an alternator repair shop near you to test it. That would at least remove the most likely suspect. If you ground the end of the pod wire that hooks to the alternator - terminal, the discharge light should come on...if it doesn't, I'd look for an open in the wire, or you may not have 12v. on the pod resistor/light..on the '82, that 12v. comes from terminal H7 on the fuse/relay panel and goes to 3R on the Pod. You can check this by disconnecting the wire from the - terminal on the alternator and measuring to see if there is battery voltage on it..one probe on the wire connector and the other to ground. I think you need to have the ignition sw in the ON position to get it(Bus 15 on the fuse/relay panel). If you don't see 12v or so, then again, either an open in the wire or you have to start digging to see why there is no 12v on the pod circuitry.


I hope this is of some help. Anyone..am I missing some other likely cause of this problem?

Jim

Flormat

Thanks Jim, very good info. Where is 3R on the pod? Is R the Right connector plug on the pod? And 3 the 3rd wire over? and if so 3rd from which side? Thanks a lot Jim. I'll let you know what I find.

Flormat

I just got my alternators back from the shop. He said they are both working. So why would the alternators fail the light bulb test? Here is how I did the test. Connected one light bulb wire to the positive terminal of the alternator. Disconnected the negative wire from pod to alternaotr and connected the other light bulb wire to the neg terminal of the alternator. Started the car and the light bulb stayed lit. Also when I tried to ground the wire from the pod to the alternator the discharge light did not come on.
I was looking for the 12v wire to the cluster volt meter. I looked at the Right side plug wire #3 which is green with a red stripe. The fuse/ relay plug H7 is black. So I think I'm looking at the wong #3 wire to the cluster. What do you think?

Flormat

I just got my alternators back from the shop. He said they are both working. So why would the alternators fail the light bulb test? Here is how I did the test. Connected one light bulb wire to the positive terminal of the alternator. Disconnected the negative wire from pod to alternaotr and connected the other light bulb wire to the neg terminal of the alternator. Started the car and the light bulb stayed lit. Also when I tried to ground the wire from the pod to the alternator the discharge light did not come on.
I was looking for the 12v wire to the cluster volt meter. I looked at the Right side plug wire #3 which is green with a red stripe. The fuse/ relay plug H7 is black. So I think I'm looking at the wong #3 wire to the cluster. What do you think?

jim morehouse

I'm stumped on this. Are there any other 928 owners in your area? You might try one of your alternators on their car. I still don't understand how the alternator tests bad on the car w the marker light and good at the shop. The only other thing I can think of is to have another shop test the alternator or, if you've got a good 928 shop nearby, have them test it on a car if they can.

I'll try to look at the pod wiring later and see if I can help you on it.

Wish I could say I understood this..good luck,
Jim

WallyP

The only possibilities that I can think of are:

The the tester that you are using is not letting enough current thru to energize the field, so the alternator isn't kicking off. Try repeating the test with a couple of changes. Get someone to help you, with them inside the car and you underneath the car. Disconnect the small exciter wire from the alternator, leaving the large battery wires connected. Hook the tester to the exciter terminal and the battery terminal. Using alligator clips or just holding it on, temporarily hook a short piece of insulated wire (at least 18 gage) from the battery terminal to the exciter terminal. Have your helper crank the engine, rev it to 2000 rpm and hold it there for thirty seconds. When the engine goes to 2000 rpm, hold the wire on the terminals for five or ten seconds and then remove it. See if the tester light is off or on. If it is off, the alternator works, at least to some extent.

The only other possiblity that I can think of is that there is some bad connection or wire in your battery/ground circuit that is screwing up the alternator. My first suspicion would be the ground strap from the engine to the chassis - but i don't see how it could alow the atarter to work but not the alternator.

jim morehouse

To add to what Wally just posted. What size bulb are you using in the tester? (I assume you're using a side marker light as in the write-up). Too low a wattage bulb would limit the current you could draw through the tester to the coil. A 3W bulb should be OK.

The writeup doesn't mention wire gauge for the tester but Wally makes a good point that you need to use something that won't add too much resistance. A simple thing that would be good enough is some old lamp cord..I think you need around 200 ma or more into the alternator coil and this should be good for around an amp or so for a 100w lamp so it won't be limiting the current. If you have an ammeter function on your multimeter, you might want to use it series w the tester to assure yourself that you're getting sufficient current into the coil...make sure your ammeter is rated for at least 300ma though.

HTH,
Jim