Strange Voltage Drop/Fluctuation

[df2x4]

So here's a weird one. Last night while I was driving my Suburban I noticed that while sitting in gear idling with my foot on the brake, my headlights would flicker and dim slightly along with the engine idle. Turned on my interior lights and they all do the same, cluster and everything. As soon as I step on the gas it evens out. On to issue number two. Whenever I use any accessory the lights dim and I get a pretty good voltage drop on the gauge. Windows, door locks, hazards, you name it. Same result with every switch I hit. This issue is persistent whether the engine is running or not. Now for the kicker. I let it sit on my trickle charger overnight and took it to two different places this morning to have the battery and alternator tested, they both tested fine at both locations. My connections at the battery are very clean and 100% corrosion free. Could this be a cable or ground strap issue? Would upgrading my big 3 cables be a possible solution? Any info would be awesome, let me know if there's some other info that would be pertinent here. Thanks in advance.

 

[magimerlin]

Before spending any money try this... bolting all your grounds you can find 1 at a time of course so you don't loose track of them and clean them real well and bolt them back down.. 3 main ones are. Battery to intake.... head to firewall.... battery to frame... there are many more but those are your main grounds...

 

[Scrufdog]

the big 3 will likely fix this, as well as make everything else happy

 

[df2x4]

Thanks for the input, guys. Haven't had a chance to work on it yet, but considering it's probably a ground issue I'm just going to go ahead and re-do my big 3 in 0ga wiring. I'm in the process of building a subwoofer box for it so that's probably a good idea anyway.

 

[df2x4]

So almost six years later...

Never did the big 3, never built the subwoofer box. The voltage fluctuation turned out to be a failing alternator. It never tested bad but obviously something was wrong with it. Not sure what it was exactly that went bad but eventually the alternator started making a ton of bearing noise so I replaced it. So far my voltage fluctuation issues have not come back.

 

[Dman1987]

@df2x4 good to know, how bad was the voltage actually fluctuating?

I installed a new alt a few months ago and I did not notice any light fluctuations but with a voltmeter it is constantly sweeping from 14.3v-14.7v

I have 2ga ofc weling wire on all main powers and grounds, and run a huge odyssey extreme battery.

for now I am considering adding a capacitor somewhere in system but ran across this post and was curios if your issue was similar to mine

 

[df2x4]

@df2x4 good to know, how bad was the voltage actually fluctuating?

I never actually measured it, but it was enough that I could see it in the interior lighting. Just slightly, it wasn't a severe strobe effect or anything. Just a slight pulse in the lights at idle. If I were running LEDs instead of standard incandescent bulbs I probably would have never seen it.

 

[1997]

So almost six years later...

Never did the big 3, never built the subwoofer box. The voltage fluctuation turned out to be a failing alternator. It never tested bad but obviously something was wrong with it. Not sure what it was exactly that went bad but eventually the alternator started making a ton of bearing noise so I replaced it. So far my voltage fluctuation issues have not come back.

thx for posting the solution.
dead threads are big on my rant list