Weird Voltage Issue

[Aloicious]

do you have underdrive pulleys installed?

I don't have UD pulleys but mine used to do most of that, only at idle, I did the big 3 too and it didn't really help much, I thought it was the alternator (after all it was the stock alt, and when the problem was happening, the alt was the original one), so I ended up swapping it out for a 180A alt with a custom pulley (a slightly undersized alt pulley, ONLY the alt pulley though, all others were and still are stock), and as soon as I swapped the alt out, the problem completely disappeared, I don't know if it was because the new alt was higher powered than the stock one, or if the original alt was on its way out or something. but the new one has been working great for the last ~3-4 years or so.

 

[BOTTLEDZ28]

I know this thread is a year old but I also have the same exact problem as the OP has. I had my alternator checked on my truck yesterday and it was putting out 55 amps under load and 81 w/o. I have a Optima red top which is holing 13.7 volts. I am in the middle of making my own custom headlight harness and I will post back here with my results so that other members can see what is working for others to try and fix this issue.

 

[silverado13]

I had the exact same problem with mine when it was stock. and then recently I put in under drive pulleys on the crank . I didn't like were the voltage is so I put an underdrive pulley on the alternator. now with the truck running and all the accessories off , the truck runs at 14 volts perfectly fine but as soon as I turn on the ac it drops down if depending on the fan speed , I figure with the underdrive alternator pulley that wouldn't be the same problem but maybe it's just the ground I plan on whenever I get some good weather going in checking all the grounds making sure they're good connection. that and I don't know if the underdrive pulleys or even worth it considering I spent about 150 dollars on both of them combined

 

[Tony_SS]

I have this problem, especially with the blinker deal on my MONTE.!

It's driving me nuts trying to find out why... Also, volts drop good when I use the power windows...

 

[addiction2bass]

old thread.... but stock gauge sucks! try another voltage display on your truck wired into the cig lighter plug or battery wire what ever. my old truck gauge dipped like crazy but the gauge just sucked. i slapped in a digital voltage display thats way more accurate and showed no problems.