Electrical Guru needed

[Heron]

Sorry, 4th thread on this truck but I was advised to start new threads..

Trying to figure this starter situation out from another thread but this is a whole new issue:

I've got a disconnect on the ground of my battery in the truck to disconnect at night as to avoid any electrical fires in my garage.

I've had this issue before the disconnect and tested the battery with the neg cable attached to the end of the disconnect and it works as expected.

So, I go to test my solenoid wire and find when I test the lead directly to the top of the negative terminal with the disconnect on(chasis and tranny ground not working) I get a full 12v with key on

But, when I turn off the disconnect and allow it to ground to the transmission and chasis the voltage drops to .05V, same thing on my glow plug circuit.

If I test the battery by itself and test with the ground at the battery or at either the transmission or chasis it tests the same as the ground at the battery. (grounds good)

Summary:

Starter is not in and starter cable not attached to anything(other than hot going back to fuse box)

1. Battery tests good at all locations including disconnect and two grounds; transm and chasis
2. Solenoid wire tests at 12v if I connect ground lead directly to battery terminal but if I turn disconnect off(allowing tranny and chasis to ground) and check it then at any location, terminal,disconnect, chasis/tranny cable then I get .05 Volts at not only solenoid wire but also glow plug strip...
3. If I put the ground lead on battery terminal, ground to tranny and chasis off(disconnect on), test the solenoid wire I get 10v with key off, key on ,I get 12volts
4. If I put ground lead on battery post with ground to terminal with disconnect on(chasis and tranny ground not connected) on and I touch engine, transmission etc...I get minimal voltage readings as if the tranny and motor are energized.

Is this a ground issue perhaps behind the fuse box or some other type of short(relay, ign switch)?

I feel it is more than likely a ignition switch...could be the cause of my exciter wire/charging light staying on. Something positive has shorted to ground. I have removed the plug from alternator

Could it have something to do with my glow plug relay? I've read about that shorting and causing all kinds of issues(truck starts immediately. virtually no delay with no cold start advance)

Just tested the 3 prong alternator wire(it has two reds and a blue):
All 3 had 12 volts!  I'm not thinking the blue wire should be 12v...correct?

I then removed the fusible link to the alternator and now there is no more weird voltage on the engine, transmission but there is also no voltage at all on the solenoid wire when the key is off, on or the start position...the starter is still not hooked up.

I apologize for the madness...took me 5x to get this straight on here..I thought this would be an easy project 

[TylerDurden]

So, I go to test my solenoid wire and find when I test the lead directly to the top of the negative terminal with the disconnect on(chasis and tranny ground not working) I get a full 12v with key on

But, when I turn off the disconnect and allow it to ground to the transmission and chasis the voltage drops to .05V, same thing on my glow plug circuit.

If I test the battery by itself and test with the ground at the battery or at either the transmission or chasis it tests the same as the ground at the battery.

This is consistent with the alternator exciter wire being shorted. Voltage drop through a diode is around .5V.

It might not be the only problem, but you gotta start somewhere and you know the exciter wire needs to be addressed. I'd pull it out of the cluster connector or just clip it close enough to splice new wire to it.

At this stage, I'd pull out the fusebox (it should just have a dozen big connectors on the back)... if the fusebox looks swollen, it may have gotten wet and corroded inside. Having the fusebox out will also give you a good view of the wiring to check for damage from mice, water, or professional mechanics.

[Heron]

Is there any trick to fusebox removal? Is it covered well in the Bentley?

I may start with the alternator plug side b/c when I unplugged the hot from the battery to the alternator(at the fusible link) all of the points like the head stopped testing for voltage. So, something having to do with that particular wire has a bearing on the situation...i think.

[TylerDurden]

Not well covered in the Bentley, I'm afraid...

If you can post a pic of the fusebox, that might help. It's been a few years since I had my caddy and I don't know/remember if it was a westy.

[Heron]

Not well covered in the Bentley, I'm afraid...

If you can post a pic of the fusebox, that might help. It's been a few years since I had my caddy and I don't know/remember if it was a westy.

Fuse box was one screw, worked it out of the tabs. Rats nest of wires but no corrosion or damage except 18 guage wire from what looks like the horn that needs some attention.

Okay, redid this post since earlier today:

Checked all wires, no issues from fusebox to alternator.

As I said earlier I have a Motorola alternator with one plug; two reds one blue exciter.

When all is hooked up except alternator plug I test with ground probe on ground of battery but battery ground not hooked to chasis or tranny=

Pos side of tester on anything, block, strut towers= No voltage readings

When all is hooked up and I plug up alternator plug and check the exact same way as above I now have voltage everywhere, block, strut tower, tranny...

Even though Autozone said the alternator is good I'm thinking I must have a short in the alternator transferring voltage to alternator housing and the rest of the block, tranny etc...

Now, if I hook up the chasis, tranny ground to the battery and then with ground side of probe on battery terminal and test the block, head, tranny I get some quick spikes of volts..     Thoughts on internal short on the alternator...

[TylerDurden]

Sure, it could be a shorted diode pack.

I would first test the blue (exciter wire) to make sure it's not shorting to ground: With the key on (engine not running), the light should be illuminated when the alternator plug is in, when the alternator plug is out, the indicator lamp should not illuminated. With the key off, there should be no voltage at the blue wire, with the key on there should be voltage, slightly less than the battery voltage.

I would test that the alternator case is grounded to engine>chassis>battery (neg).

I would make some 10ga jumper wires with spade terminals to go between the plug and the alternator, then with the red wires jumpered between the plug and the alternator, I'd run the engine and momentarily jumper 12v to the field terminal (where the blue wire connects) rev the engine like usual and meter the output red wires... no voltage means bad alternator.

[Heron]

The charging light would not go off originally. Between starter issues and charging lt not going off started me down this road.
There is and has never been a ground strap on this alternator..and there were never issues.

If the diode pack can short that must be what it is. The two red wires stay hot but should not tranfer voltage to the alternator shell. Hence all is fine when its not plugged up but as soon as its plugged in the alternator along with the engine and tranny test for vo!tage and the vo!tage goes right into the exciter wire when its plugged in along with the two red wires.
Am I on the right track?

[TylerDurden]

The tests I described above in post #5 are pretty conclusive, if performed.

Metering the chassis/block/alternator case should show voltage, since there are connections from the positive to electrics in the vehicle like the clock/radio/etc. that have connection to ground. I get the same results on my 86 Jetta.

[Heron]

The tests I described above in post #5 are pretty conclusive, if performed.

Metering the chassis/block/alternator case should show voltage, since there are connections from the positive to electrics in the vehicle like the clock/radio/etc. that have connection to ground. I get the same results on my 86 Jetta.

I will run the tests, my starter has been giving me issues..not sure if that is part of the issue.

Couple of questions before I run the other tests:

If the key is off, two red wires plugged to alternator and I test the blue wire(cut right now) coming out of the plug that is attached to the alternator I have 9-10volts. With exciter wire disconnected from alternator there is no light on the dash like there was before.

With the all three wires plugged up I now have voltage everywhere and on the solenoid wire with the key off
Yet, if I disconnect blue wire, I have no voltage at the solenoid wire with key off-- starter works perfectly..no spinning and clunking.
So, should the blue wire coming out from the plugged in-plug have voltage with the key off?
Is this voltage backfeeding into the cluster and such causing starter issues and exciter light to be on?
Thx much for the help!

[ORCoaster]

This voltage on the blue wire sounds all wrong.  I was under the impression that the exciter wire was only providing voltage when the alternator is running.  Not with the key off. 

Sure sounds like something is fouled up with the blue wire.  Shorted to ground from mouse chewing?   

This makes me want to pull out the voltmeter and go pop the hood on my 81 for you but the sun just set and I would only have 15 mins of daylight left.  Not enough to really get started as I don't have a garage space to work in.  Maybe tomorrow if it is sunny.

[Heron]

Sure, it could be a shorted diode pack.

I would first test the blue (exciter wire) to make sure it's not shorting to ground: With the key on (engine not running), the light should be illuminated when the alternator plug is in, when the alternator plug is out, the indicator lamp should not illuminated. With the key off, there should be no voltage at the blue wire, with the key on there should be voltage, slightly less than the battery voltage.

I would test that the alternator case is grounded to engine>chassis>battery (neg).

I would make some 10ga jumper wires with spade terminals to go between the plug and the alternator, then with the red wires jumpered between the plug and the alternator, I'd run the engine and momentarily jumper 12v to the field terminal (where the blue wire connects) rev the engine like usual and meter the output red wires... no voltage means bad alternator.

Exciter wire:
Alternator plugged up, key on , light illuminated
Unplug it, key on and no light
Key on: 11.3 volts at the exciter wire, grounded terminal on neg battery post
Key off: No volts at exciter wire

Resistance measured at alternator .13...Ground okay

No charging when running with light illuminated and engine revving.

Jumper 12v from battery to exciter wire at plug and now CHARGING!

So, just under 12 volts like you said on the exciter wire with key on but how would less then one volt make a difference?

Next step?

[Heron]

This voltage on the blue wire sounds all wrong.  I was under the impression that the exciter wire was only providing voltage when the alternator is running.  Not with the key off. 

Sure sounds like something is fouled up with the blue wire.  Shorted to ground from mouse chewing?   

This makes me want to pull out the voltmeter and go pop the hood on my 81 for you but the sun just set and I would only have 15 mins of daylight left.  Not enough to really get started as I don't have a garage space to work in.  Maybe tomorrow if it is sunny.

Checked the exciter wire all the way thru and looks perfect. If you look at the above post I did what Tyler suggested and found I had just less than 12 v with the key on. I was checking it before without the battery grounded to the tranny and chasis. I was getting volt readings all over the motor and all but Tyler had said that was normal. So, when I rechecked with all grounds connected to the batter and my tester on the post I got different readings.. I like auto electric about as much as plumbing, although since I've done more plumbing it sure is easier. 
Now I'm really confused.
Alternator is good but my exciter wire is not carrying enough voltage with the key on to trip the field. But all the connections look good where the blue wire connects into the cluster. I even tightened up the 7mm screws on the back of the cluster that I read someone had luck with that.

[TylerDurden]

Next step?

I would add my black jumper cable from the alternator case to the neg post on the battery along with the normal cables. If the charging system and alternator light work properly, the ground path back to the battery is suspect.

Typically, I use a 2ga neg battery cable directly to a bolt holding the tranny to the block.

If the car was kept in a coastal region, the salt in the air can cause corrosion everywhere.

[RustyCaddy]

At the risk of not being very helpful. Recently, after the car had been sitting a couple of weeks while getting an injection pump and fueling issue sorted out, the charging light wouldn't go off when i revving the the trucks engine.  Nothing had been changed with the electrical system except the ignition switch had been replaced several months before without any new and/or associated problems cropping up.  It took about 3 miles of driving before the light went off, something it had never done before and hasn't done since.  The truck already had the alternator case grounded to the battery directly (like the starter).  i might have missed it but am not sure if you have been able to take the car for a short drive?

These cars do strange and un-explainable things; it can get a bit crazy. May be put the light issue on the back burner, relax and watch a game or two, till you can drive it around the block a couple three times?

[TylerDurden]

Now I'm really confused.
Alternator is good but my exciter wire is not carrying enough voltage with the key on to trip the field.

The blue wire is notorious for internal breaks near the alternator.

Voltage is just one aspect, the wire has to carry enough current... a wire with some broken strands might show voltage on a meter but not carry enough current to do the job.

With the key off, there should be no voltage at the blue wire or the D+ terminal on the alternator where it connects.