| the Alternator Story [message #175256] |
Sun, 01 July 2012 20:46  |
1275gtsport
Messages: 272
Registered: September 2009
Location: Rothesay NB
Karma: 0
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After doing a search on the forum I have so far checked most of the connections from Battery to Alt and followed (part) of the trouble shooting steps in the Shop manual.
The fusible link has just about melted a bit on one end it seems to still have continuity but may not be passing full current.
I am am reading the Manual correctly it says that I should do a static check of the ALt BAT terminal that it should read close to what the Battery is reading at the post.
If that is right, will the fusible link being melted cause a voltage drop? I seem to be getting .34 volts from the BAT terminal on the ALT and the Battery is around 12.7
and for more "info" I have no dash lights, did not have any before leaving on the trip, and the 10 amp fuse for the gauges is not blown. I also do not have an indicator that the high beams are on.
Also when I turn the Ign key to accessory the non-working temp gauge (PO installed after market gauge) pegs to hot. It stays in the cold position when the engine is running. when I was pressing the boost switch the oil pressure gauge would jump up just a little over the width of itself. but the other gauges did not move. (sounds like no ground to the instrument panel)
Just for testing can I replace the link with a 10 amp fuse? I will get a fusible link to replace.
Any thoughts on what may have caused the fusible link to melt?
Adam Raeburn
Rothesay, NB
1976 Austin Mini
1977 GMC Palm Beach
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Once you replace everything that is attached to something else. It will all be fixed.
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| Re: the Alternator Story [message #175265 is a reply to message #175256] |
Sun, 01 July 2012 21:51  |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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I would recommend that your fusible link be replaced
with a new 16 ga fusible link, just like it had before.
A fuse has different characteristics than a fusible link.
Whenever you change something from stock, you run the
risk of getting stranded.
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: the Alternator Story [message #175274 is a reply to message #175256] |
Mon, 02 July 2012 01:44 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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First you will NOT read 12 volts at the "bat" terminal on the alternator when the engine is NOT running. This is because the isolator is in between the battery and the alternator. The isolator is a diode or one way check valve. On a car where there is no isolator what the book says is true. Those two locations (battery and alternator bat terminal) should be about the same.
Note: If you REPLACE the isolator with a combiner then one of the things that is required is to wire the alternator to the engine battery side of the system and you will then read 12 volts at the alternator "bat" terminal with the engine not running just like a GM car.
Repair or better yet replace that fusible link. I have seen several of them age and open or intermittently open up. All current (except the starter and charging the battery from the alternator) goings to the rest of the engine of the coach flows through that fusible link. A 10 amp fuse there will not replace a bad fusible link. I very short term fix for a bad fusible link could be a short piece of 16 gauge wire. I would not leave it in there long as I do not know the melting characteristics or current capability of regular wire vs. fusible link wire.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: the Alternator Story [message #175275 is a reply to message #175274] |
Mon, 02 July 2012 01:53 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I read some more of your posting regarding the dash lights. The dash lights are controlled by turning the rheostat in the headlight switch. That rheostat get's its ground through it's mounting to the aluminum plate. I had a problem once with mine where the mounting although tight had oxidized and was no longer making an electrical connection. A more common failure is the wire grounding that plate comes loose or oxidized. There is a wire from that plate running up front to the aluminum plate that has the boost solenoid and isolator mounted on it. Then there is a second wire running from that isolator plate direct to the negative battery terminal. Check both of these wires.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: the Alternator Story [message #175366 is a reply to message #175256] |
Mon, 02 July 2012 20:55 |
1275gtsport
Messages: 272
Registered: September 2009
Location: Rothesay NB
Karma: 0
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OK I have determined the Alt is not producing any power. I do have the same (or very close to the same voltage) as the battery on the BAT post of the Alt. - have sent alt for rebuild.
Will also get fusible link replaced.
As for no dash lights. checked ground and cleaned. -still no work.
Ken the second ground to the neg terminal what gauge should it be? there is nothing but the ground cable connected to the Neg terminal of the battery.
Adam Raeburn
Rothesay, NB
1976 Austin Mini
1977 GMC Palm Beach
---------------------------------------------------
Once you replace everything that is attached to something else. It will all be fixed.
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| Re: the Alternator Story [message #175379 is a reply to message #175366] |
Mon, 02 July 2012 22:36 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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The 1975 GMC wiring diagram shows that wire between the battery and the front aluminum plate as being a 14 gauge black one. You could also use 12 gauge black. Another option would be to run that wire through the black split tubing loom near the isolator tubing running back to the engine and connecting it direct to any bolt on the engine block. There is less chance of it getting corroded or knocked off of the battery and it shortens the path to the master ground of the coach which is the engine block.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] the Alternator Story [message #175411 is a reply to message #175379] |
Tue, 03 July 2012 10:20 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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It sounds to me like the rheostat incorporated into the headlamp/dash
light switch that dims the dash lamps has failed, or the grounding of the
switch is faulty. The headlamp switches are available, and not too
difficult to change. Also, as an aside, the grey wire that is found several
places in the instrument panel area, is for the express purpose of dimming
the instrument cluster lamps. Make sure that someone has not mistakenly
used it for the ground wire. It would cause problems similar to the ones
you are having.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Mon, Jul 2, 2012 at 8:36 PM, Ken Burton <n9cv@comcast.net> wrote:
>
>
> The 1975 GMC wiring diagram shows that wire between the battery and the
> front aluminum plate as being a 14 gauge black one. You could also use 12
> gauge black. Another option would be to run that wire through the black
> split tubing loom near the isolator tubing running back to the engine and
> connecting it direct to any bolt on the engine block. There is less chance
> of it getting corroded or knocked off of the battery and it shortens the
> path to the master ground of the coach which is the engine block.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
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| Re: the Alternator Story [message #175538 is a reply to message #175256] |
Wed, 04 July 2012 18:15 |
1275gtsport
Messages: 272
Registered: September 2009
Location: Rothesay NB
Karma: 0
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Have been side tracked with another project. (but I can now walk through the garage again).
Alternator came back from the rebuilder with a brand new pulley and bearings and from what I can tell he simply reused my outer case to hold all the new parts. the GEN light comes on when the key is first turned on and goes out when the engine starts. I haven't had a second to double check what the voltage is when it is running as it started raining as soon as I crawled under the front to install the beast.
I do see a grey wire that is not connected to anything and may have gone to the original radio. it is not grounding to anything but not providing any power either. will look at that tomorrow.
I don't want my "new" alt to cook if the reason it went before was no dash lights (or a short in there).
Adam Raeburn
Rothesay, NB
1976 Austin Mini
1977 GMC Palm Beach
---------------------------------------------------
Once you replace everything that is attached to something else. It will all be fixed.
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| Re: the Alternator Story [message #175560 is a reply to message #175256] |
Wed, 04 July 2012 21:09 |
1275gtsport
Messages: 272
Registered: September 2009
Location: Rothesay NB
Karma: 0
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Senior Member |
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When I put a known 12 volt supply to the Grey wire the dash lights all light. would that indicate that the light switch needs to be replaced or that the grey wire needs to be attached to something?
Can I buy the switch at a local parts store? I suppose I could go look in my parts book.
Adam Raeburn
Rothesay, NB
1976 Austin Mini
1977 GMC Palm Beach
---------------------------------------------------
Once you replace everything that is attached to something else. It will all be fixed.
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| Re: the Alternator Story [message #175572 is a reply to message #175560] |
Thu, 05 July 2012 02:20 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| 1275gtsport wrote on Wed, 04 July 2012 19:09 |
When I put a known 12 volt supply to the Grey wire the dash lights all light. would that indicate that the light switch needs to be replaced or that the grey wire needs to be attached to something?
|
The gray wire at the radio plug is a supply to the light INSIDE the OEM radio.
SO... putting power to that wire and having the dash lights come on, means that the dash lights, themselves are fine. ... so is the ground on the other side of the lights.
Seems you are not getting power to, or through, the headlight switch and potentiometer. (Try turning the knob.)
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: the Alternator Story [message #175573 is a reply to message #175572] |
Thu, 05 July 2012 02:31 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Mike Miller wrote on Thu, 05 July 2012 00:20 |
| 1275gtsport wrote on Wed, 04 July 2012 19:09 |
When I put a known 12 volt supply to the Grey wire the dash lights all light. would that indicate that the light switch needs to be replaced or that the grey wire needs to be attached to something?
|
The gray wire at the radio plug is a supply to the light INSIDE the OEM radio.
SO... putting power to that wire and having the dash lights come on, means that the dash lights, themselves are fine. ... so is the ground on the other side of the lights.
Seems you are not getting power to, or through, the headlight switch and potentiometer. (Try turning the knob.)
|
Note that I am ASS-U-Me'ing that the reason you applied power to the gray wire at the radio, was that you where troubleshooting a "no dash lights" problem.
If I assumed wrong: Just cap it off. Very few after-market radios can use this lead.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] the Alternator Story [message #175611 is a reply to message #175601] |
Thu, 05 July 2012 10:16 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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At this point I would guess that you have a bad rheostat on the headlight switch.
To get the headlight switch out you first have to turn it on by pulling the know all the way out. Then reach under the dash and depress a small button on the bottom (or top if someone installed it upside down). This will allow you to pull the knob and shaft out of the switch. Then unscrew the nut holding the switch to the dash panel. Pull down on the body of the switch and you can then unplug the connector and take the switch out from below the dash.
If the rheostat coil is burned it should be readily apparent or you can test it with a VOM.
The switches are readily available from about any autoparts store as they were used for many years on almost all GM vehicles.
NAPA HL6554SB or HL6613SB
Borg Warner S427
Standard DS155
Autozone Wells SW144
Emery Stora
77 Kingsley
Frederick, CO
On Jul 5, 2012, at 8:36 AM, 1275gtsport@gmail.com wrote:
>
>
> OK I have no dash lights when I pull the headlight switch. twisting does nothing until it clicks over and lights the dome light (which works on the drivers side only)
>
> Yes I was simply trouble shooting the no dash lights which is why I powered the grey wire. it is now cut off and taped will never speak of grey wire again :)
>
> I noticed that the dash light fuse is a 20 amp I don't have a 10 amp on hand but will replace with a 10 amp right away.
>
> If I can't find what ground is missing I will start a new thread on the dash lights.
>
> Thanks for all the input.
>
> off to try and get the holding tank to dump. if it ain't one end its the other:)
> --
> Adam Raeburn
> Rothesay, NB
> 1976 Austin Mini
> 1977 GMC Palm Beach
> ---------------------------------------------------
> Once you replace everything that is attached to something else. It will all be fixed.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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