PG01
Supporting Member
Keeping them alive, love it.
Voltage meter fluctuation with turn signals?
- Thread starter derekjl
- Start date
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I've had three '99 Tahoes and this is a '95 with the 350 TBI. I wouldn't have it any other way. Had 66k miles on it, one owner, practically stole it from the only owner.
Could you do me a huge favor? Can you check the behavior of the voltage gauge when you turn the hazards on? I've noticed the most fluctuation when they are on. It's even worse when the rear defroster is on. If you turn the blower fan high enough you will notice the fan also fluctuates a little bit with the rhythm of the hazards. Is this really considered normal? I can't check the output of the alternator right now because the weather is so bad, below zero here for the next couple of days.
east302
Full Access Member
I have two of these trucks, a 98 Z71 and a 98 Tahoe, so it helps being able to compare.
This is the dash gauge on the truck with blower on high, hazards on and all accessories on, including rear defrost.
Corresponding alternator voltage is 14.39V, so the gauge is reasonably accurate considering that the tick marks are not intuitive.
If we are to assume some inkling of linearity, then the mark halfway between 9 and 14 would be 11.5, the other one being 16.5. I kind of call BS on the accuracy at that point.
This is what a real voltage gauge would look like. You would be able to tell, at a glance, what the voltage value is without resorting to doing a math problem in your head.
Anyways, back on topic.
The truck’s gauge does not fluctuate with the turn signal. It has a one year old battery, five year old alternator and original battery cables.
Now the Tahoe is where I see it quiver a little. It has a new battery, new alternator and new cables. Here’s the gauge on it with blower on high and with all lights, hazards, rear defrost and accessories on. Corresponding alternator voltage is 14.69V.
With the hazards, lights, defrost and blower on high, it quivers a little - no more than one minor tick mark, whatever that span is supposed to represent on the gauge. I hear no variance with the blower speed which is drawing full battery voltage when on high. Alternator output during all of that varies by 2 to 4/100V on my meter, so I think that is ok given the varied system demand when the signals are on.
For me, I think the cluster is the issue.
Once you guys thaw out, putting a meter on your alternator would be the next step. You may have something pulling too much. Check the drop across the alternator cable first. I believe that anything more than 0.1V is an issue.
I’d turn everything off and, while watching the voltage at the battery, turn accessories on one at a time to see if you spot the culprit.
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This is the dash gauge on the truck with blower on high, hazards on and all accessories on, including rear defrost.
Corresponding alternator voltage is 14.39V, so the gauge is reasonably accurate considering that the tick marks are not intuitive.
If we are to assume some inkling of linearity, then the mark halfway between 9 and 14 would be 11.5, the other one being 16.5. I kind of call BS on the accuracy at that point.
This is what a real voltage gauge would look like. You would be able to tell, at a glance, what the voltage value is without resorting to doing a math problem in your head.
Anyways, back on topic.
The truck’s gauge does not fluctuate with the turn signal. It has a one year old battery, five year old alternator and original battery cables.
Now the Tahoe is where I see it quiver a little. It has a new battery, new alternator and new cables. Here’s the gauge on it with blower on high and with all lights, hazards, rear defrost and accessories on. Corresponding alternator voltage is 14.69V.
With the hazards, lights, defrost and blower on high, it quivers a little - no more than one minor tick mark, whatever that span is supposed to represent on the gauge. I hear no variance with the blower speed which is drawing full battery voltage when on high. Alternator output during all of that varies by 2 to 4/100V on my meter, so I think that is ok given the varied system demand when the signals are on.
For me, I think the cluster is the issue.
Once you guys thaw out, putting a meter on your alternator would be the next step. You may have something pulling too much. Check the drop across the alternator cable first. I believe that anything more than 0.1V is an issue.
I’d turn everything off and, while watching the voltage at the battery, turn accessories on one at a time to see if you spot the culprit.
Sent from my iPhone using Tapatalk
Last edited:
I have two of these trucks, a 98 Z71 and a 98 Tahoe, so it helps being able to compare.
This is the dash gauge on the truck with blower on high, hazards on and all accessories on, including rear defrost.
Corresponding alternator voltage is 14.39V, so the gauge is reasonably accurate considering that the tick marks are not intuitive.
If we are to assume some inkling of linearity, then the mark halfway between 9 and 14 would be 11.5, the other one being 16.5. I kind of call BS on the accuracy at that point.
This is what a real voltage gauge would look like. You would be able to tell, at a glance, what the voltage value is without resorting to doing a math problem in your head.
Anyways, back on topic.
The truck’s gauge does not fluctuate with the turn signal. It has a one year old battery, five year old alternator and original battery cables.
Now the Tahoe is where I see it quiver a little. It has a new battery, new alternator and new cables. Here’s the gauge on it with blower on high and with all lights, hazards, rear defrost and accessories on. Corresponding alternator voltage is 14.69V.
With the hazards, lights, defrost and blower on high, it quivers a little - no more than one minor tick mark, whatever that span is supposed to represent on the gauge. I hear no variance with the blower speed which is drawing full battery voltage when on high. Alternator output during all of that varies by 2 to 4/100V on my meter, so I think that is ok given the varied system demand when the signals are on.
For me, I think the cluster is the issue.
Once you guys thaw out, putting a meter on your alternator would be the next step. You may have something pulling too much. Check the drop across the alternator cable first. I believe that anything more than 0.1V is an issue.
I’d turn everything off and, while watching the voltage at the battery, turn accessories on one at a time to see if you spot the culprit.
Sent from my iPhone using Tapatalk
Appreciate your detailed response. It seems the accessory that "kills" mine the most is the rear defrost. I did some searching and it isn't all that uncommon. I guess because so much current is sent through the glass. However, I've noticed that when it does drop, it will come right back up to 14.xx volts in a second or so. The only thing that will cause it to stay lower than that is pushing all of the window switches on the driver's door at once, same with all of my other Tahoes in the past. Weather is going to be much better this week so I will take my meter and test as you mentioned, will report back then. I'm sure I'll have an answer as to whether or not there is a real voltage change.
Kelsda
Full Access Member
View attachment 190840
what brand of alternator,sure you have the correct one I believe some came with a 105 amp.and so on
Here’s mine new ac delco alternator 4 year old battery everything on even extra lights 4 55 watt halagons hazards moved needle like a hair pulsing back and fourth other wise holding steady at 14 in photo put in drive foot on brake went a hair below 14 half way still touching 14 maybe dirty connectionsView attachment 190840
Last edited:
I also have a brand new AC Delco unit. I'm positive it is the correct one. I cross-referenced it with the GM part # as well as my VIN. It is AC Delco 335-1023, basically it's the standard 105 amp version. Mine generally does stay right at 14 volts, maybe even a very small amount over, which is what it's supposed to do. Still have yet to test the voltage at the battery, will do so when the weather doesn't suck.
east302
Full Access Member
Hey, did you sort this out?
I noticed my blower speed decreasing when stopped at a light with my turn signal on. I’m starting to think I may have an issue like yours.
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I noticed my blower speed decreasing when stopped at a light with my turn signal on. I’m starting to think I may have an issue like yours.
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I didn’t yet. Will let you know via this thread. Try something else. When in Park, turn your blower on high and put your hazard lights on. I can hear my blower slow down and go back to normal when the flashers go on/off/on/off, etc. I’m leaning towards a ground issue as others have mentioned. I’m going to soon upgrade the battery as well. NAPA leaves a sour taste in my mouth from past experiences and 690 CCA just isn’t enough in this part of the country when we get well below zero in the winter.
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east302
Full Access Member
It isn’t obvious with the hazards on and doesn’t do it all of the time, but it only does it when in drive. Not in park - the engine speed comes up and it makes it up.
With foot on brake, in drive, hazards on, blower on high and all accessories on, the alternator voltage gets down to 12.9V. It’s a 105A alternator.
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With foot on brake, in drive, hazards on, blower on high and all accessories on, the alternator voltage gets down to 12.9V. It’s a 105A alternator.
Sent from my iPhone using Tapatalk
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