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Roger and I have an exciter wire question

 
Old 11-16-2007, 01:21 PM
  #16  
dr bob
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Follow Alan's test procedure and report back what you see. The symptom where you see voltage at the exciter terminal with key off tells me it's coming from the alternator. With the exciter lead lifted you can prove or disprove this. At the same time, make sure you have voltage at the exciter lead with key on, lead disconnected from the alternator. No volts on that lead with key off, still disconnected. With these hints you can decide where the voltage is coming from.

If you installed an alarm system in the car that taps into the ignition-on (15) bus, ---unplug--- the alarm module so it's completely disconnected, and see if the dash light symptom goes away. It may also go away with the exciter lead disconnected from the alternator, so try that first.
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Old 11-16-2007, 02:27 PM
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Originally Posted by Jim bailey - 928 International View Post
Odds are the front engine harness is toast ! The big alternator power feed wire to the jump start post and oil pressure wire as well as starter wires are bundled together. The insulation has cracked and wires are cross feeding. That often happens after it is worked on and the harness moved around like during a timing belt change.
Jim - I have wondered about that. The thickest of the red wire housings was cracked a bit. I wrapped the opening in electrical tape during the alternator installation. Had to do the same with the oil level sensor cable.

Originally Posted by dr bob View Post
Follow Alan's test procedure and report back what you see. The symptom where you see voltage at the exciter terminal with key off tells me it's coming from the alternator. With the exciter lead lifted you can prove or disprove this. At the same time, make sure you have voltage at the exciter lead with key on, lead disconnected from the alternator. No volts on that lead with key off, still disconnected. With these hints you can decide where the voltage is coming from.
Bob - an interesting test. Indeed the source of the voltage is the alternator, not the exciter wire. In neither key position case did a test between the detached exciter wire and a ground source other than the alternator housing yield any voltage. There is no voltage to the exciter wire.

The alternator itself showed 12.6V when grounded no matter where I touched the meter stick to on the alternator. 12.6V from main terminal to ground. 12.6V from housing to ground. Both with key out and key in second position.

Voltage between main terminal and exciter wire was less than 12.6V with key in our out - about 9V.

Weird?

Meanwhile, I have pulled the pod and investigated the wiring behind it. My recently installed ignition switch was a little loose, but the above tests were done after I tightened it. Please note pic.

Thanks big time.
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Old 11-16-2007, 08:10 PM
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The alternator itself showed 12.6V when grounded no matter where I touched the meter stick to on the alternator. 12.6V from main terminal to ground. 12.6V from housing to ground. Both with key out and key in second position.

The 12.6 volts from housing to ground kinda scares me. The alternator housing needs to be at ground potential, bolted securely to the alternator console (mounting bracket) which is bolted to the engine block, which is grounded to the car frame/body by a braided copper ground strap between the block on the right side and the right side frame rail. So there can be no potential between the housing and ground. Can you clarify where you were measuring?
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Old 11-16-2007, 11:02 PM
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Originally Posted by dr bob View Post
The 12.6 volts from housing to ground kinda scares me. Can you clarify where you were measuring?
Bob:

Roger and I did a little testing on the instrument panel this afternoon. My understanding is that both the alternator resistor and the alternator gauge light have to be working in order for the exciter circuit to fire.

Resistor Tested continuity - fine. Measured the resistance to be about 71.5 ohms.

Bulb I transplanted a 12V/1.2A bulb socket from another location in the instrument cluster.

When I then turned the key to the ignition point, the following happened:

1. All the gauge lights quickly flashed on as should be except the alternator gauge light

2. After about two seconds, the central warning light started to flash, along with the oil pressure light. (It's been doing that all afternoon)

3. Still with the key to ignition, I measured voltage between the exciter post and ground -- 12.6V. Voltage between main terminal and ground -- 12.6V. In fact, voltage from any metal area on the alternator to ground -- 12.6V!

I then removed the key and tested voltage again:

4. 12.6V from any place on the alternator and ground except
5. 0V between exciter post and ground!

In all cases I used the adjustment screw bracket as the ground point. So it seems that there was some evidence that the exciter circuit was firing. But it simply caught up to an existing 12.6V that existed throughout the alternator.

What an interesting gremlin...
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Old 11-16-2007, 11:09 PM
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Are you saying that there is a direct short to the alternator body? If there is, the alternator is grounded so that would leave a direct short to ground throughout the car.
Obviously I must be misunderstanding something here.
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Old 11-16-2007, 11:21 PM
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Originally Posted by Charley B View Post
Are you saying that there is a direct short to the alternator body? If there is, the alternator is grounded so that would leave a direct short to ground throughout the car.
Obviously I must be misunderstanding something here.
Well that would make at least two of us. From what little I know, I would expect 0V differential between the alternator and ground when the key is out.
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Old 11-17-2007, 12:14 AM
  #22  
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Originally Posted by dr bob View Post
Follow Alan's test procedure and report back what you see. The symptom where you see voltage at the exciter terminal with key off tells me it's coming from the alternator. With the exciter lead lifted you can prove or disprove this. At the same time, make sure you have voltage at the exciter lead with key on, lead disconnected from the alternator. No volts on that lead with key off, still disconnected. With these hints you can decide where the voltage is coming from.

If you installed an alarm system in the car that taps into the ignition-on (15) bus, ---unplug--- the alarm module so it's completely disconnected, and see if the dash light symptom goes away. It may also go away with the exciter lead disconnected from the alternator, so try that first.
This is a good idea but I think the alarm worked fine and did not interfere with the ignition bus. If you want to eliminate this, pull the two wires from the t-taps at A2 and A5 ( the two A- connectors). Since you had problems before the alarm system and the alarm worked fine, I don't think there are any internal faults in the system. Best of luck.
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Old 11-17-2007, 12:31 AM
  #23  
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Originally Posted by [email protected] View Post
This is a good idea but I think the alarm worked fine and did not interfere with the ignition bus. If you want to eliminate this, pull the two wires from the t-taps at A2 and A5 ( the two A- connectors). Since you had problems before the alarm system and the alarm worked fine, I don't think there are any internal faults in the system. Best of luck.
Hey Dave!
I too don't think that the alarm system is involved here. But just to be sure, I will temporarily pull the t-tap wires. Are these the Yellow and GreenBlack t-taps?

Peace,
Tim
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Old 11-17-2007, 12:35 AM
  #24  
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Well that would make at least two of us. From what little I know, I would expect 0V differential between the alternator and ground when the key is out.
Well I'll leave it to the experts here, but I should think there would be zero volts between the alternator casing and ground even if the car is running.
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Old 11-17-2007, 12:40 AM
  #25  
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Originally Posted by 84totheFloor View Post
Hey Dave!
I too don't think that the alarm system is involved here. But just to be sure, I will temporarily pull the t-tap wires. Are these the Yellow and GreenBlack t-taps?

Peace,
Tim
No. They are they taps on the central fuse panel connectors, all the way to the left of the passenger footwell panel. The connector has all the really big wires into it. Check you connection sheet that I made for you and the labels on the harness. They are labeled in the diagram as constant 12V and ignition on. Again, I'm not concerned, so if you are unsure, just forget for now. Call me if you are still unsure.
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Old 11-17-2007, 01:22 AM
  #26  
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Yes Tim you have to investigate the alternator casing - it must be grounded - without this solid ground the alternator cannot generate power....

The alternator case must always be at ground and the main terminal must always be at battery voltage.

The exciter terminal with exciter wire attached should be at 0v with ignition off and at a low voltage with ignition on and engine not running and at ~battery voltage when the car is running an the alternator operating normally.

Something seems very odd here...

Alan
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Old 11-17-2007, 03:39 AM
  #27  
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The exciter wire, when disconnected, has to be 0v relative to ground with the key off. It should be ~11v with the key on; the resistor and light bulb work together to achieve this voltage drop.

When connected, you should see 0v at the exciter wire with the key off and 8-10v with the key on -- the additional voltage drop is because the alternator is now hooked up.

The two wires in your photo -- is there continuity from either of those to the exciter wire?

The fact that you are not seeing the alternator light when you first turn the key indicates that the exciter wire is not connected(any of the connections along the way, incl. the bulb socket) or the bulb is bad.

The fact that you are describing +12.6v at the alternator body indicates that "what we have here, is a failure to communicate".

Please either take some pics or lift whatever you need from here, edit the pics in paint to illustrate what you're doing exactly, and post the pic(s) here.
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Old 11-17-2007, 11:47 AM
  #28  
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I think I can explain the dash behaviour here...

For whatever reason the exciter wire (61) is getting driven to 12v without the alternator generating any output.

The dashboard enters bulb test mode when the igniton is first turned on - it exits bulb test mode after the car starts and the exciter line reached 12v as the alternator starts generating. In this case the exciter is already at 12v so bulb test terminates almost immediately. The dash and central warning now think the car is running - but there is no oil pressure...

Test the exciter wire off the alternator. If its 0v with key off and 12v with key on - seems to me the whole source of the problem is the alternator.

Connect the 2 big alternator cables together with a bolt with the alternator fully removed. Start the car on the battery - does everything run normally? No dash warnings?

If so change the alternator

Alan
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Old 11-17-2007, 01:08 PM
  #29  
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Originally Posted by Alan View Post
I think I can explain the dash behaviour here...

For whatever reason the exciter wire (61) is getting driven to 12v without the alternator generating any output.

The dashboard enters bulb test mode when the igniton is first turned on - it exits bulb test mode after the car starts and the exciter line reached 12v as the alternator starts generating. In this case the exciter is already at 12v so bulb test terminates almost immediately. The dash and central warning now think the car is running - but there is no oil pressure...

Test the exciter wire off the alternator. If its 0v with key off and 12v with key on - seems to me the whole source of the problem is the alternator.

Connect the 2 big alternator cables together with a bolt with the alternator fully removed. Start the car on the battery - does everything run normally? No dash warnings?

If so change the alternator

Alan

Dude, you are unbelievable

Here's my homework as suggested by you and Dave A.
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Old 11-17-2007, 01:37 PM
  #30  
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Alan,
Would this have anything to do with the originall alternator being a 90 amp Valero and the replacement being a 90 amp Bosch?
I swaped a Paris Rhone 90 amp on my 82 with the replacement Bosch 90 amp - no problem.
I have another new remanufactured Bosch alternator ready to ship to Tim. Are we going to get the same problem. Is there any way to test the alternator?
Roger
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