Lights dimming at idle. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tdp67 · 12-13-2010, 12:59 PM

When the truck is at idle the head lights and dash lights dim. Whae I give it gas they come back. Anyone know a possible cause? Could it be battery or charging system? Maybe I need to clean the battery trminals?

Allensracing · 12-13-2010, 01:08 PM

what year is the truck? or more importantly, what alternator are you using? it used to be normal for the charging system to not keep up at idle. those 35 amp alternators cant keep the headlights going at idle
it sounds like the alternator is not giving enough juice at low rpm

tdp67 · 12-13-2010, 01:10 PM

Quote:

Originally Posted by Allensracing

what year is the truck? or more importantly, what alternator are you using? it used to be normal for the charging system to not keep up at idle. those 35 amp alternators cant keep the headlights going at idle
it sounds like the alternator is not giving enough juice at low rpm

Sorry, forgot to mention it's a 67 with a 350 crate in it. Not sure about the alternator. How do I tell?

Allensracing · 12-13-2010, 01:11 PM

do you have the original style alternator with an external regulator?
there should be a model style and amperage rating on the side of the alternator.

tdp67 · 12-13-2010, 01:12 PM

Can you tell by the pics?

tdp67 · 12-13-2010, 01:13 PM

Quote:

Originally Posted by Allensracing

do you have the original style alternator with an external regulator?
there should be a model style and amperage rating on the side of the alternator.

I don't think any of it is original.

Allensracing · 12-13-2010, 01:15 PM

I see a plug on the back with a blue and white wire. is it aiming straight back to the firewall, or is it aiming up towards the hood?

cdowns · 12-13-2010, 01:19 PM

those rubber gas lines are an excellent source of nice big fires//i'd worry about that first

tdp67 · 12-13-2010, 01:32 PM

Quote:

Originally Posted by Allensracing

I see a plug on the back with a blue and white wire. is it aiming straight back to the firewall, or is it aiming up towards the hood?

I'll look when I get home.

tdp67 · 12-13-2010, 01:33 PM

Quote:

Originally Posted by cdowns

those rubber gas lines are an excellent source of nice big fires//i'd worry about that first

That sounds scary! What are they supposed to be?

Allensracing · 12-13-2010, 01:35 PM

I dunno, even the factory uses rubber fuel lines. just make sure its "fuel" and not something else written on the line

I have changed a few to steel braided line, and they can leak also

red71cheyenne · 12-13-2010, 01:42 PM

From the looks of it, thats a one wire alternator and they all are bad about not putting out enough amps at idle. The best way to get around it is to upgrade to a CS130 alternator. There are a few FAQ's on it on the Electrical FAQ on how to do it.

I had the same issues when I went to a one wire alternator and upgrading solved my problems. You might want to see if your voltage regulator is bypassed or not, as the newer style you have does not use the external regulator. Its on the core support below the driver's side headlight. The plug should have jumpers on it to bypass the output voltage of the alternator.

cdowns · 12-13-2010, 01:45 PM

Quote:

Originally Posted by tdp67

That sounds scary! What are they supposed to be?

GM produced about a gizillion with metal fuel lines, have seen many home brew rubber ones burn to the ground over the past 40 years or so but never one with a nice metal fuel line

Allensracing · 12-13-2010, 01:49 PM

Red, if my memory serves me, the blue and white wires are the factory alternator control wires. that looks to me like the original alternator with an external regulator. it is hard to tell from the picture, but there is nothing else up there for the blue and white wires.

red71cheyenne · 12-13-2010, 01:55 PM

Quote:

Originally Posted by Allensracing

Red, if my memory serves me, the blue and white wires are the factory alternator control wires. that looks to me like the original alternator with an external regulator. it is hard to tell from the picture, but there is nothing else up there for the blue and white wires.

Right, but that isn't the original alternator. Thats a chrome one and usually they are the one wire versions nowadays. If the blue and white wires go to the external voltage regulator, it can be made to work properly, just not sure on how to do that. If your voltage regulator has been bypassed then those two wires serve no purpose other than filling the hole on the alternator. You will have to verify that the regulator is still wired for operation and not bypassed. If it is wired right, then you can start the engine and check the output voltage at the battery with a voltmeter to see what the regulator is putting out at idle. Could be that its time for a new regulator. They do go bad after 30+ years.

Allensracing · 12-13-2010, 02:01 PM

looks to me like someone polished the original alternator. it looks like the shape of the external regulator style.

tdp67 · 12-13-2010, 02:07 PM

I'm pretty sure by the VIN that this was originally a 6 cyl. Wouldn't that be a different alternator?

Allensracing · 12-13-2010, 02:12 PM

Quote:

Originally Posted by tdp67

I'm pretty sure by the VIN that this was originally a 6 cyl. Wouldn't that be a different alternator?

the alternators themselves are interchangeable. the external regulator and internal regulator are identical how they bolt up, with the exception of the location of the two prong plug.
the brackets for a 6 cyl are different from a v8
when you get home, take a picture of the back of the alternator. that will pretty much tell all.
has this problem always been there, or is it new?

tdp67 · 12-13-2010, 02:15 PM

Quote:

Originally Posted by Allensracing

the alternators themselves are interchangeable. the external regulator and internal regulator are identical how they bolt up, with the exception of the location of the two prong plug.
the brackets for a 6 cyl are different from a v8
when you get home, take a picture of the back of the alternator. that will pretty much tell all.
has this problem always been there, or is it new?

I haven't driven it much since I got it and even less at night. I think it may have always done it.

rusty baker · 12-13-2010, 02:17 PM

Are you sure that the belt is tight? That could be a simple answer.

**VetteVet** · 12-13-2010, 02:19 PM

here you go.

tdp67 · 12-13-2010, 02:19 PM

Quote:

Originally Posted by rusty baker

Are you sure that the belt is tight? That could be a simple answer.

No, I'll have to look at that as well, Thanks

fixit-p · 12-13-2010, 03:16 PM

External reg 10DN alternator.

12SI internal reg alternator.

**LockDoc** · 12-13-2010, 03:28 PM

-
I lightened his picture up a little so it would be easier to see.

lockDoc

red71cheyenne · 12-13-2010, 05:35 PM

It looks exactly like the 100amp one wire I had on my 71 that did the same thing until I upgraded to CS130.

12-13-2010, 12:59 PM	#1
tdp67 Registered User Join Date: Apr 2010 Location: Rowlett, TX Posts: 325	Lights dimming at idle. When the truck is at idle the head lights and dash lights dim. Whae I give it gas they come back. Anyone know a possible cause? Could it be battery or charging system? Maybe I need to clean the battery trminals? Last edited by tdp67; 12-13-2010 at 01:00 PM.

12-13-2010, 01:08 PM	#2
Allensracing Registered User Join Date: Dec 2010 Location: Paradise, ca Posts: 295	Re: Lights dimming at idle. what year is the truck? or more importantly, what alternator are you using? it used to be normal for the charging system to not keep up at idle. those 35 amp alternators cant keep the headlights going at idle it sounds like the alternator is not giving enough juice at low rpm __________________ Last edited by Allensracing; 12-13-2010 at 01:09 PM.

12-13-2010, 01:11 PM	#4
Allensracing Registered User Join Date: Dec 2010 Location: Paradise, ca Posts: 295	Re: Lights dimming at idle. do you have the original style alternator with an external regulator? there should be a model style and amperage rating on the side of the alternator. __________________

12-13-2010, 01:12 PM	#5
tdp67 Registered User Join Date: Apr 2010 Location: Rowlett, TX Posts: 325	Re: Lights dimming at idle. Can you tell by the pics? Attached Images

12-13-2010, 01:15 PM	#7
Allensracing Registered User Join Date: Dec 2010 Location: Paradise, ca Posts: 295	Re: Lights dimming at idle. I see a plug on the back with a blue and white wire. is it aiming straight back to the firewall, or is it aiming up towards the hood? __________________

12-13-2010, 01:19 PM	#8
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Lights dimming at idle. those rubber gas lines are an excellent source of nice big fires//i'd worry about that first __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY Last edited by cdowns; 12-13-2010 at 01:20 PM.

12-13-2010, 01:35 PM	#11
Allensracing Registered User Join Date: Dec 2010 Location: Paradise, ca Posts: 295	Re: Lights dimming at idle. I dunno, even the factory uses rubber fuel lines. just make sure its "fuel" and not something else written on the line I have changed a few to steel braided line, and they can leak also __________________ Last edited by Allensracing; 12-13-2010 at 01:36 PM.

12-13-2010, 01:42 PM	#12
red71cheyenne Back in the sticks Join Date: Jan 2001 Location: Fordland, MO Posts: 3,188	Re: Lights dimming at idle. From the looks of it, thats a one wire alternator and they all are bad about not putting out enough amps at idle. The best way to get around it is to upgrade to a CS130 alternator. There are a few FAQ's on it on the Electrical FAQ on how to do it. I had the same issues when I went to a one wire alternator and upgrading solved my problems. You might want to see if your voltage regulator is bypassed or not, as the newer style you have does not use the external regulator. Its on the core support below the driver's side headlight. The plug should have jumpers on it to bypass the output voltage of the alternator. __________________ 1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty

12-13-2010, 01:49 PM	#14
Allensracing Registered User Join Date: Dec 2010 Location: Paradise, ca Posts: 295	Re: Lights dimming at idle. Red, if my memory serves me, the blue and white wires are the factory alternator control wires. that looks to me like the original alternator with an external regulator. it is hard to tell from the picture, but there is nothing else up there for the blue and white wires. __________________

12-13-2010, 02:01 PM	#16
Allensracing Registered User Join Date: Dec 2010 Location: Paradise, ca Posts: 295	Re: Lights dimming at idle. looks to me like someone polished the original alternator. it looks like the shape of the external regulator style. __________________

12-13-2010, 02:07 PM	#17
tdp67 Registered User Join Date: Apr 2010 Location: Rowlett, TX Posts: 325	Re: Lights dimming at idle. I'm pretty sure by the VIN that this was originally a 6 cyl. Wouldn't that be a different alternator? Last edited by tdp67; 12-13-2010 at 02:07 PM.

12-13-2010, 02:17 PM	#20
rusty baker '70 C-10 Primer Join Date: Dec 2008 Location: nevada,missouri Posts: 117	Re: Lights dimming at idle. Are you sure that the belt is tight? That could be a simple answer. __________________ "The difference between stupidity and genius is that genius has its limits." Albert Einstein

12-13-2010, 02:19 PM	#21
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,718	Re: Lights dimming at idle. here you go. Attached Images __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

12-13-2010, 03:28 PM	#24
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,774	Re: Lights dimming at idle. - I lightened his picture up a little so it would be easier to see. lockDoc Attached Images __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

12-13-2010, 05:35 PM	#25
red71cheyenne Back in the sticks Join Date: Jan 2001 Location: Fordland, MO Posts: 3,188	Re: Lights dimming at idle. It looks exactly like the 100amp one wire I had on my 71 that did the same thing until I upgraded to CS130. __________________ 1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty



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