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Re: [GMCnet] Help near Springfield, MO [message #326581 is a reply to message #326580] Fri, 01 December 2017 10:51 Go to previous messageGo to previous message
johnd01 is currently offline  johnd01   United States
Messages: 354
Registered: July 2017
Location: Sacrameot
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Senior Member
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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Johnd01 John Phillips Avion A2600 TZE064V101164 Rancho Cordova, CA (Sacramento)

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