Lights dimming at idle.

[tdp67]

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]

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]

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?

[tdp67]

Can you tell by the pics?

[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.

[tdp67]

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]

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]

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

[tdp67]

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?

[cdowns]

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

[tdp67]

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.

[Allensracing]

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]

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]

Originally Posted by Allensracing

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

yep factorys cheap cheap with rubber lines// just saw this morning VW is recalling half million carz cause rubber fuel lines r burnin up VW's
in 50 years haven't seen a recall on metal fuel lines burnin up cars

sometimes the little extra money and effort is worth it over something quick n cheap

[shrike]

try this: http://www.madelectrical.com/electri...adlights.shtml

Not necessarily that company, but putting relays on your headlights will greatly affect their brightness. If you read that article, he will explain exactly why.

[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.

[red71cheyenne]

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]

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

[tdp67]

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

[Allensracing]

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]

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]

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

[mr48chev]

Originally Posted by Allensracing

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

That is what it looks like to me too.

It won't make any difference between six or 8 cylinders but if you have added accessories to the truck the alternator may not be able to keep up with the power demand at an idle.

A bit of explanation. Most of these trucks didn't have many accessories to draw a lot of electricity and they ran the regular headlights that didn't draw as much power as the halogen lights we run most of the time now. Start the truck, put the charge back in the battery, keep up with the am radio and headlights and off down the road with maybe the wipers going or the heater fan blowing. Now days we have Halogen lights, a big stereo with an amp behind or under the seat and a full set of speakers and maybe AC to go along with that and the little 35 amp alternator can't keep up with the demand some times.

If the lights just go dim at low speeds and then everything is ok and the truck always starts I wouldn't get too excited but if you start having starting problems because the load is more than the output of the alternator and the battery is being drained when you run down the road rather than being charged it may be time for a bigger alternator.

[tdp67]

I guess my next question is, where is the best place to buy one of these at a good price?

[VetteVet]

here you go.