Weird Voltage Issue

[moviewithnotitle]

Background:
1996 Tahoe 2dr. 5.7L, Auto, A/C, 4x4, Single battery.
My battery and Alternator are both good. Charging is right at 14volts when running. 12.6V with engine off. I have a Optima Red top that is 1yr old. I have a 105A alternator that is two yrs old. All wiring is clean (meaning no corrosion) on the battery terminals and in most places I check like grounds and connections.

Problem:
- When I turn on the headlights, the volt gauge on the dash dips a bit, and stays there.
- When I turn on the blower/fan, the volt gauge on the dash dips a bit, and stays there.
- When I turn on the the headlights and blower, the volt gauge on the dash dips a down alot, and stays there.
- When I turn on the headlights and the turn signal, the volt gauge on the dash will dip when in sync with the turn signal.

Conclusions...
1. I suspect this is a ground issue on a main wiring harness. I have corrosion or a bad connection somewhere that I don't suspect to be bad. I have done some due diligence on the grounds on the frame, motor, battery etc, but can't seem to find the root of the cause. All wires look good there too.
2. I don't suspect the gauge is bad, as it will read normal on an everyday basis.

Has anyone experienced anything like this or have a few thoughts about what might be causing this based on my descriptions?

Thanks,
MWNT

 

[95TwinTT]

It sounds like your alternator is not able to keep up. I would remove the alternator and take it to a shop that rebuilds starters and alternators and have it tested. They have the equipment to check amperage output at different speeds, etc.

Could be the regulator inside the alternator.

 

[blueflamed03]

agree, those were always suspect to be able to handle any load, over time. I say upgrade to a larger output and you will be fine. Sounds like it's doing the best voltage out it can.

 

[steamroller]

Big 3 upgrade + 145 amp AD244 alternator

 

[96ProCompTahoe]

having a similar problem with the camaro. new battery, alt, big three, terminals. still eventually runs dead after driving/starting it a few times.

yet to find the problem, but it is a pain in the ass.

 

[moviewithnotitle]

having a similar problem with the camaro. new battery, alt, big three, terminals. still eventually runs dead after driving/starting it a few times.

yet to find the problem, but it is a pain in the ass.

That sounds like a bad relay not charging back to the battery.

 

[95TwinTT]

Here is a simple test for you guys. If you show 14 volts when idling and the voltage drops when you turn on the heavy amperage items, like headlights, rear window defogger, heater fan, etc. Raising the rpm’s of the engine should help the voltage come up.

If the voltage does not come up all the way to 13.5 to 14 volts with higher rpm’s, the alternator is not able to keep up with the “draw”. It would be doubtful it would be a grounding issue if it is repeatable.

You can have a 80 amp alternator that only puts out 40 amps. The shops that work on these things can actually make alternators that put out specific amps at various rpms to match your needs.

Alternator shops can often do a quick test on a alternator while you wait. Find them in the yellow pages in your town.

I have a local shop that took my 80 amp alternator up to a 140 amp, using the same case. They also generally use quality components as apposed to the “rebuilt” alternators from Mexico and beyond.

My Tahoe would never go over 12.5 volts mostly because of all the electrical equipment I added to the rig. Now it stays at 14 all the time It’s running, no matter what I turn on or off, with my new rebuilt alternator…

It’s only a couple of bolts to yank it off to go and get it checked……………………

It also does'nt hurt to up the gauge of the wire from the alternator to the battery......

 

[96ProCompTahoe]

battery ususally shows within range of voltage, but the guage on the dash has damn well never even been close, haven't pulled the dash or anything yet but have yet to come across anything either.

first alternator came back low output after 2 shops tested it, second one tested fine before i put it in, battery tested fine (but it is a red-top, thats been on the charger a few hundred times now) upgraded the big 3. everything in the car is stock...

 

[95TwinTT]

battery ususally shows within range of voltage, but the guage on the dash has damn well never even been close, haven't pulled the dash or anything yet but have yet to come across anything either.

first alternator came back low output after 2 shops tested it, second one tested fine before i put it in, battery tested fine (but it is a red-top, thats been on the charger a few hundred times now) upgraded the big 3. everything in the car is stock...

If you are sure the battery and alternator are OK,

You need to get a meter that can measure DC amperage. (Radio Shack has a decent one for $30). Unhook one side of the battery and put the meter between the post and the unhooked cable and see what the amperage draw is, with everything OFF.

If the draw is over 50 to 60 milliamps, start pulling relays one at a time to see if you can isolate the problem. If you can’t find it with relays, go for the fuses.

 

[moviewithnotitle]

Follow-up...
I did the Big 3 upgrade this weekend. I also included an upgrade to the charging wire from the alternator. Charging is identical, and most of the original issues remain. One thing I did notice is that there is an additional ground for the headlights(Source of a lot of voltage fluctuation). It looks pretty weak and old and in need of replacement. I hope to get to that upgrade this week. I'm setup now to add a 2nd battery and upgrade the alternator too and will do so within the next few weeks.