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Re: [GMCnet] Help near Springfield, MO [message #326582 is a reply to message #326581] Fri, 01 December 2017 11:01 Go to previous messageGo to previous message
James Hupy is currently offline  James Hupy   United States
Messages: 6806
Registered: May 2010
Karma:
Senior Member
That is why I told him that BOTH his isolator, and internal regulator in
the alternator are bad, also told him to check sense wires for continuity
by isolating them and checking each end of both wires. That eliminates any
outside influence from affecting his meter readings. Golly, I hate
supposedly rebuilt aftermarket alternators. So does my rebuilder, but they
bring him a lot of business.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Dec 1, 2017 8:52 AM, "John Phillips" wrote:

> If the sense wire goes to the chassis battery the isolator would cause the
> problem.
>
> On Fri, Dec 1, 2017 at 8:40 AM, James Hupy wrote:
>
>> Tom, you have more wrong than a bad isolator. Center tap and ground
> should
>> show 14.5 or so. Both top and bottom taps should show .7 volts less than
>> that. 20 volts idling tells me that your engine alternator has a bad
>> internal regulator, OR the sense wires have an open circuit ( those are
> the
>> two wires that plug into the alternator ) trace those down and check for
>> continuity on both of them when they are disconnected from the circuit.
>> Frequently, they have a second 2 pin connector buried in the wire loom
> that
>> goes across the front of the engine near the upper thermostat housing.
> Age
>> and heat and vibration all take their toll.
>> Jim Hupy
>> Salem, Or
>> 78 GMC ROYALE 403
>>
>> On Dec 1, 2017 8:03 AM, "Emery Stora" wrote:
>>
>> Shut it down! Way to high voltage on the bottom! You’ll ruin your
>> batttery.
>>
>> Yes, it looks like a bad isolator.
>>
>> Emery Stora
>> 77 Kingsley
>> Frederick, CO
>>
>>> On Dec 1, 2017, at 8:45 AM, Tom Lins wrote:
>>>
>>> Tom Lins wrote on Thu, 30 November 2017 18:53
>>>> Ken Burton wrote on Thu, 30 November 2017 17:33
>>>> > Tomtom wrote on Thu, 30 November 2017 15:18
>>>> >> Do you have a hand held voltmeter? If so, I'd check the voltage
>> across the battery and the voltage at the center position of the diode
>>>> >> isolator pack (I think this is the lead that goes to the
> alternator).
>> The isolator diodes will give a half a volt or more voltage drop I
>>>> >> think.
>>>> >>
>>>> >> Tom
>>>> >
>>>> >
>>>> > Tom is entirely correct here is some more info.
>>>> >
>>>> > Read the voltage at the isolator WITH THE ENGINE RUNNING. Use the
>> aluminum plate that the isolator is mounted on for your negative meter
> lead
>>>> > connection. Any cheap volt meter will work. (Harbor Freight,
> Walmart,
>> Sears, etc.) The center terminal of the isolator should read around 14.7
>>>> > volts. The top and bottom terminals should read around 14.0 volts.
>>>> >
>>>> > If those voltages are correct read the voltage across the battery.
> It
>> also should be around 14.0 volts.
>>>> >
>>>> > Without the above voltage numbers, here are my best guesses.
>>>> > 1. Loose plug in back of the alternator
>>>> > 2. Bad replacement alternator.
>>>> > 3. Bad isolator
>>>> > 4. Blown fusible link
>>>> > 5. Blown "GEN" light in the dash causing the alternator not to
> start.
>> Does the GEN light turn on with the key on and prior to starting?
>>>> >
>>>> > Good Luck. The above are just guesses until we get more information.
>>>>
>>>> Ken
>>>>
>>>> The voltages were all about what you are saying are correct
>>>> I really think the dash gauge was not wired correctly, The PPO
> installed
>> CIP deluxe dash
>>>> the one with the 4 gauges either side of the Speedo and Tach and I am
>> not 100% convinced everything is
>>>> wired correctly. There are several other switches on the side panel
> for
>> the 2 large electric fans
>>>> in front of the radiator and one to trigger the halon fire
> extinguisher
>> by the engine.
>>>>
>>>> He also installed a second air compressor in the Electro Level system
>> that needs to be turned on
>>>> with a separate switch and it appears to be hooked to the house
> battery
>> system.
>>>> The EL system is acting odd and only seems to be able to maintain
> normal
>> ride height
>>>> As long as it can do that until we get home I will look at that when
> we
>> get home.
>>>>
>>>> And yes the gen light does come on before you start it.
>>>
>>>
>>>
>>> Ken
>>>
>>> I made a stupid mistake. I measured the voltage with the engine running
>> but forgot I was plugged into shore power
>>> This morning in daylight I tried again with the coach disconnected with
>> the engine running. Up to running temp and idleing
>>> the voltage on the isolater are as follows
>>>
>>> Top 11.8
>>> Center 20
>>> Bottom 19.1
>>>
>>> Chassis Battery reads 11.8 from the hot to the plate the isolator is
>> mounted to.
>>>
>>> Bad isolator?
>>>
>>> --
>>> Tom Lins
>>> Elkton, FL
>>> 77 GM Rear Twin
>>>
>>>
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>
>
>
> --
>
> *John Phillips*
> _______________________________________________
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