Generator light in dash stays on - The 1947 - Present Chevrolet & GMC Truck Message Board Network

c10crazy · 07-30-2005, 03:48 PM

In a plain 69 cluster, what would cause the generator light to stay on?. I put a tester on the battery and got 12.5 volts. I did the key off drain test with a tester and have had no problems. Any ideas?

jhow66 · 07-30-2005, 04:18 PM

Stays on with key off or when running?

Longhorn Man · 07-30-2005, 04:22 PM

was that 12.5 with the engine running??

c10crazy · 07-30-2005, 04:36 PM

jhow66- stays on when driving
Longhorn man- that was with the engine off

Longhorn Man · 07-30-2005, 04:44 PM

what does the read with the engine on? The light will always be on with the ignition switch on and the engine off.

If it is on when the engine is running, it is supposed to mean you aren't charging.

c10crazy · 07-30-2005, 04:48 PM

I'll have to test it with the engine on to see what it reads voltage wise. When I'm driving down the road it stays on all the time.

Longhorn Man · 07-30-2005, 05:22 PM

You may not be charging.

On my old '70 longhorn, the light stayed on, and for no reason. Since I had installed after market guages under the dash (I don't trust 35 year old dummy lights) I just ripped the bulb out and called it good. (after verifying it was in fact charging)

jhow66 · 07-31-2005, 12:06 AM

This might help:

c10crazy · 08-01-2005, 08:13 AM

Thanks for the pic. How do I test my alternator to see if it's bad???

jhow66 · 08-01-2005, 10:09 AM

Quote:

Originally Posted by c10crazy

Thanks for the pic. How do I test my alternator to see if it's bad???

Take it to one of the parts stores-AutoZ--Advance etc.

1968GMC · 08-01-2005, 11:40 AM

do this test. undo your - battery post, then with a test light toutch the - post and with the other end of test light toutch the unhooked batt cable. If the light on tester lights up uou got a short somewhere
While the light is lit up, unplug the voltage regulator. If light goes out then thats your probleme.

c10crazy · 08-01-2005, 11:53 AM

I did the test light trick to check for a drain and it didn't light up. Can I use a multimeter on the alternator to check to see if it's bad?. If so, how?

Longhorn Man · 08-01-2005, 09:34 PM

That test light deal only helps to locate a drain, not a faulty charging system.
Fire up the truck, and just place the leads on the battery. If it is less than 13, then you need to do more troubleshooting.
Placing the lead on the large red wire on the back of the alt will give you the same reading as on the battery, but the battery is easier to get to when the engine is running.

c10crazy · 08-01-2005, 09:54 PM

Well, I went to drive the truck today and it wouldn't start up

. Last weekend I had to give it a hot shot and then it was fine. The battery is only 2 years old. The regulator looks fairly new but the alternator looks nasty. I put the battery on a 3 hour charge and it reads 13.5 volts sitting on the workbench. I think I'll take the alt. in to test it and go from there. I always heard something about starting the truck and while it's running disconnect one of the cables and if it dies it's the alternator. Is this dangerous to do?

Robert1970C20rstbukt · 08-01-2005, 10:00 PM

It's only dangerous if you let the pos. cable touch a ground when you do that with the engine running. I've done it before to check the alternator on my truck and I'm still alive.

c10crazy · 08-01-2005, 10:05 PM

which cable am I supposed to remove when it's running?

Longhorn Man · 08-01-2005, 10:37 PM

The cable test will only tell 1/2 truths. If your alt is only putting out one amp, your engine will still run at an idle.
You can remove either cable, but the neg cable is safer to remove.

68haywagon · 08-01-2005, 11:51 PM

:andy:

Longhorn Man · 08-02-2005, 12:03 AM

LOL, my computer was messin up...I had thought the board went down again.

motocrosschump · 08-02-2005, 09:29 AM

Mine stayed on when my Coil was tightened down good enough..

07-30-2005, 03:48 PM	#1
c10crazy Like a Rock! Join Date: May 2002 Location: USA Posts: 1,092	Generator light in dash stays on In a plain 69 cluster, what would cause the generator light to stay on?. I put a tester on the battery and got 12.5 volts. I did the key off drain test with a tester and have had no problems. Any ideas? __________________ 69 LWB Runs great - work in progress Mess with me and you mess with the whole trailer park!

07-30-2005, 04:18 PM	#2
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Stays on with key off or when running? __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

07-30-2005, 04:36 PM	#4
c10crazy Like a Rock! Join Date: May 2002 Location: USA Posts: 1,092	jhow66- stays on when driving Longhorn man- that was with the engine off __________________ 69 LWB Runs great - work in progress Mess with me and you mess with the whole trailer park!

07-30-2005, 04:48 PM	#6
c10crazy Like a Rock! Join Date: May 2002 Location: USA Posts: 1,092	I'll have to test it with the engine on to see what it reads voltage wise. When I'm driving down the road it stays on all the time. __________________ 69 LWB Runs great - work in progress Mess with me and you mess with the whole trailer park!

07-31-2005, 12:06 AM	#8
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	This might help: Attached Images __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

07-30-2005, 04:22 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	was that 12.5 with the engine running??

07-30-2005, 04:44 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	what does the read with the engine on? The light will always be on with the ignition switch on and the engine off. If it is on when the engine is running, it is supposed to mean you aren't charging.

07-30-2005, 05:22 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	You may not be charging. On my old '70 longhorn, the light stayed on, and for no reason. Since I had installed after market guages under the dash (I don't trust 35 year old dummy lights) I just ripped the bulb out and called it good. (after verifying it was in fact charging)

08-01-2005, 08:13 AM	#9
c10crazy Like a Rock! Join Date: May 2002 Location: USA Posts: 1,092	Thanks for the pic. How do I test my alternator to see if it's bad??? __________________ 69 LWB Runs great - work in progress Mess with me and you mess with the whole trailer park!

08-01-2005, 11:40 AM	#11
1968GMC love my truck Join Date: May 2001 Location: aylmer QC Posts: 648	do this test. undo your - battery post, then with a test light toutch the - post and with the other end of test light toutch the unhooked batt cable. If the light on tester lights up uou got a short somewhere While the light is lit up, unplug the voltage regulator. If light goes out then thats your probleme.

08-01-2005, 11:53 AM	#12
c10crazy Like a Rock! Join Date: May 2002 Location: USA Posts: 1,092	I did the test light trick to check for a drain and it didn't light up. Can I use a multimeter on the alternator to check to see if it's bad?. If so, how? __________________ 69 LWB Runs great - work in progress Mess with me and you mess with the whole trailer park!

08-01-2005, 09:34 PM	#13
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	That test light deal only helps to locate a drain, not a faulty charging system. Fire up the truck, and just place the leads on the battery. If it is less than 13, then you need to do more troubleshooting. Placing the lead on the large red wire on the back of the alt will give you the same reading as on the battery, but the battery is easier to get to when the engine is running.

08-01-2005, 09:54 PM	#14
c10crazy Like a Rock! Join Date: May 2002 Location: USA Posts: 1,092	Well, I went to drive the truck today and it wouldn't start up . Last weekend I had to give it a hot shot and then it was fine. The battery is only 2 years old. The regulator looks fairly new but the alternator looks nasty. I put the battery on a 3 hour charge and it reads 13.5 volts sitting on the workbench. I think I'll take the alt. in to test it and go from there. I always heard something about starting the truck and while it's running disconnect one of the cables and if it dies it's the alternator. Is this dangerous to do? __________________ 69 LWB Runs great - work in progress Mess with me and you mess with the whole trailer park!

08-01-2005, 10:00 PM	#15
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	It's only dangerous if you let the pos. cable touch a ground when you do that with the engine running. I've done it before to check the alternator on my truck and I'm still alive. __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck

08-01-2005, 10:05 PM	#16
c10crazy Like a Rock! Join Date: May 2002 Location: USA Posts: 1,092	which cable am I supposed to remove when it's running? __________________ 69 LWB Runs great - work in progress Mess with me and you mess with the whole trailer park!



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08-01-2005, 10:37 PM	#17
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	The cable test will only tell 1/2 truths. If your alt is only putting out one amp, your engine will still run at an idle. You can remove either cable, but the neg cable is safer to remove.

08-01-2005, 11:51 PM	#18
68haywagon I'm watching you! Join Date: Feb 2005 Location: Levittown, PA Posts: 1,822	:andy: __________________ 2012 Chevrolet Silverado 1500 Z71 4WD 1993 Chevrolet C-1500 W/T - Blue - 4.3L V-6, 4 speed auto - Dad's (RIP) 1992 Chevrolet S10 - LS swap project 1968 Chevrolet C-10 longbed fleetside - sold

08-02-2005, 12:03 AM	#19
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	LOL, my computer was messin up...I had thought the board went down again.

08-02-2005, 09:29 AM	#20
motocrosschump Registered User Join Date: May 2005 Location: Texarkana, AR 71854 Posts: 397	Mine stayed on when my Coil was tightened down good enough.. __________________ 2006 Titan SE Crew Cab Daily Driver 2005 Mazda Tribute (Wifes car) 1969 C10 SWB 350/3 Fleet "Max" 1969 Chevelle 2 door 350/3

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