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Old 11-14-2012, 10:11 PM   #1
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Need Alternator, Electrical Help

Hello! I'm new to the forum and looking for some assistance. We are the original owners of a 90 1/2 Bounder that has almost always been garaged and has only 35,000 original miles. It is a 454 engine and GM chassis.

My problem is two-fold. The guage on the dash is showing a discharge, or at least that the alternator is not charging the battery. Although I'm not sure, this COULD be caused by the fact that I may not have my wires correctly hooked up in the engine battery/coach batteries area.

I have put a voltmeter on the hot lead of the alternator and with a good ground, I'm only getting a reading of 12.45 volts at a fast idle and revving of the engine. The battery is fully charged and I have read that if so, the alternator won't charge higher. Not sure about that.

I'm at a loss. I don't want to pull the alternator unless I'm sure that is the problem. As you are aware, pulling the alternator is a bit of a nightmare.

I'm asking for some direction before I turn it over to a mechanic who will charge an arm and a leg for the alternator R&R.
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Old 11-14-2012, 10:38 PM   #2
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Being GM it may be missing the exciter voltage missing - if so, there is commonly a fuse in the exciter line that will open. Is there a battery isolator for the house vs. chassis battery? If so, the isolator could be faulty. I have had both problems with mid-90's GM chassis coaches.
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Old 11-14-2012, 11:07 PM   #3
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so what is the batt voltage with the engine off?
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Old 11-15-2012, 12:19 AM   #4
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so what is the batt voltage with the engine off?
I had charged the battery at home before installing it for the alternator test. The battery voltage was somewhere around 12.85 volts without the engine running.
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Old 11-15-2012, 12:22 AM   #5
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Being GM it may be missing the exciter voltage missing - if so, there is commonly a fuse in the exciter line that will open. Is there a battery isolator for the house vs. chassis battery? If so, the isolator could be faulty. I have had both problems with mid-90's GM chassis coaches.
I'm not sure IF or WHERE the isolator would be. I don't even know what to look for or what it looks like. Same thing with the "exciter line". Don't have a clue where to look or what it looks like.
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Old 11-15-2012, 01:01 AM   #6
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Exciter line is the (red usually) line that attaches to the back of the alternator. That line should have power to it any time the key is on.
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Old 11-15-2012, 03:26 AM   #7
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When you turn the ignition key on, are all the normal dash lights working - oil and charge warning.

You mentioned wiring alterations/disconnections. If you fired up the engine without having a load connected to the alternator (ie the battery) then it is very possible to damage the alternator.
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Old 11-15-2012, 06:23 AM   #8
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Quote:
The battery is fully charged and I have read that if so, the alternator won't charge higher. Not sure about that.
When you first start the coach it is normal for the guage to read below 13 for a minute or two but it should then stay over 13. Below 13 is not normal.
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Old 11-15-2012, 08:44 AM   #9
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I'm only getting a reading of 12.45 volts at a fast idle and revving of the engine.
12.45 is not enough to charge a battery to full. You should have a reading to around 13.2-13.9
Have the alternator rebuilt at a shop that does that.

I had to replace one that was putting out 12.5

Test it at the 12.45 and while doing that turn the headlights on brights. If it doesn't jump up and go over the 12.45. Replace
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Old 11-15-2012, 10:16 AM   #10
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There is one other test you might want to perform. On GM vehicles of that era there is a fusible link down by the starter. In newer vehicles it is located in the fuse block. You do not have to get under your vehicle to test it. Disconnect the ground cable only (-) at your battery for the chassis. Now locate the large stud on the back of the alternator, the one with the large wire attached (usually red). Using your multimeter set to ohms, touch the red lead from the multimeter to the back of the stud, and then touch the black lead to the positive terminal of the chassis battery. If the fusible link is fine, you will get a reading, if the link is blown then the meter will read the same as before you touched the two ends.
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Old 11-15-2012, 10:19 AM   #11
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Exciter line is the (red usually) line that attaches to the back of the alternator. That line should have power to it any time the key is on.
If you are talking about the MAIN red wire coming off the back of the alternator, that is the one I hooked the voltmeter to with key off and main battery connected. Then I started the engine. The reading was 12.45 volts no matter what rpm the engine was at. I got the sense that the reading was essentially the same as the battery voltage with whatever load was being applied to the battery at that point. The battery is new.
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Old 11-15-2012, 10:35 AM   #12
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Quote:
Originally Posted by Tony Lee View Post
When you turn the ignition key on, are all the normal dash lights working - oil and charge warning.

You mentioned wiring alterations/disconnections. If you fired up the engine without having a load connected to the alternator (ie the battery) then it is very possible to damage the alternator.
In answer to you first question, ALL normal dash lights are working.
Secondly, I don't believe I have started the engine without the main battery connected. However, there are OTHER wires that may require a HOT connection that were NOT connected. These are all smaller gauge wires.

BTW, there are two typical looking what I would call starter solenoids in the system. These are the kind with two larger posts ("ears") and two smaller posts, reminiscent of the type you would find on vintage Mustangs. Anyway, one is mounted in the engine compartment directly above the alternator. The other is mounted in the front battery mounting area, directly above the main engine battery. I have been unable to trace these wires completely, but the one by the alternator seems to take wires FROM the alternator, as well as from the starter. The solenoid above the main battery has red wires that I presume needs a hot connection.

I just wish I had a full-proof way of DEFINITELY determining that the problem IS the alternator and NOT some lack of a wire connection.

When I first took the coach to a local Autozone, they put a tester on the battery connection and said "your alternator is bad". Maybe it's as simple as that. I just hate to go down the labor road of pulling and replacing the alternator if THAT is not the problem in the end. And my inclination is to do the R&R myself, starting with separating the fan shroud into two halves in order to have room to work.
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Old 11-15-2012, 10:35 AM   #13
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Another thing to know about: I had a 1990 HR with the 454 motor and it had an Alt. that was a dual type and it was no longer made. Neither was the regulator. It took me a month to get an Alt. and regulator that would work. None of the newer units will work. If you run into this problem PM me and I'll try to help you out.
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Old 11-15-2012, 10:40 AM   #14
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Originally Posted by Triker56 View Post
12.45 is not enough to charge a battery to full. You should have a reading to around 13.2-13.9
Have the alternator rebuilt at a shop that does that.

I had to replace one that was putting out 12.5

Test it at the 12.45 and while doing that turn the headlights on brights. If it doesn't jump up and go over the 12.45. Replace
With the voltmeter connected to the main red lead on the back of the alternator, WITH the main battery connected and the engine running and RPMs increased, the reading was 12.45...not high enough I'm thinking. I did not turn on the lights or accessories, but I will. Other than that, did I test correctly? what if the smaller wires from the solenoid were not connected? Is that tantamount to NOT having the alternator connected to the battery? If so, maybe I HAVE damaged the alternator.
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