Occasional drop in overall voltage

[tlamot01]

I wasn't sure how to label this post, but hopefully, I'm not the only one with this type of problem.

I own a 1998 Yukon SLT. I can't recall this problem existed when I bought the truck, but sometimes, regardless of engine speed, all the electrical components seem to dim for a split second and then recover. It is very noticeable in the headlights and if I can catch it, I can see my voltmeter sweep below 12V. This only lasts for about a second and has no observable pattern.

What I've done to the electrical system since purchase:
* Alternator change to high output - Changed twice to different brands to determine if this was the cause. Still occurs
* Optima Red Top - Still no change, although it does not seem to allow the alternator to go past 12.5 volts.
* Voltage regulator - Still no change.
* Ignition coil - Still no change.
* Electric fans, but the dimming happens regardless of the fan cycling. (I can hear the fans come on, and even those have nearly no effect on the electrical system according to the voltmeter - it only drops about .25 volts)

So I'm at a loss here. I don't think it's causing any harm to the engine/computer; but still a bit annoying.

Any suggestions?

 

[SunlitComet]

Connection, Connection, Connections. Go over all your power and ground leads and check for looseness and corrosion.

 

[tlamot01]

Thanks for the suggestions. I'll check the obvious areas (battery, alternator, fuse box). Do you happen to know where (or near where) I should be looking for the remaining ground straps?

 

[SunlitComet]

GROUNDS LOCATION
G100 (VIN J, F) RH front of Intake Manifold
G101 Sheet Metal at RH front Wheelhouse
G102 RH front of Engine Block, near Damper Pulley
G103 RH front of Engine, near Thermostat Housing
G104 RH top of Cylinder Head, near center
G105 RH front of Engine Block
G107 LH front Fender (Auxiliary Battery Ground)
G110 RH rear of Engine Compartment, below Heater Lines Gill RH rear of Engine
G112 RH front of Engine Compartment, below Underhood Reel Lamp
G113 On Radiator Support, near LH Headlamp
G150 (VIN M, R, J) RH front of Engine, near Thermostat Housing
G200 Behind LH side of I/P, below Fuse Block
G201 Behind LH side of I/P, below Fuse Block
G400 RH "B" Pillar
G401 Rear of LH Framerail, behind Bumper
G403 Rear of Framerail, behind Bumper
G404 Inside LH Framerail, near rear Crossmember
G405 Frame Ground, at rear of vehicle
G410 LH Inside of Framerail, near rear Bumper
G451 At Platform Hitch

 

[99Nali]

Maybe getting a capacitor would help. -not an elect expert

 

[sparg93]

As Sunlit mentioned, definitely check those connections.

Personally, I would go through all the connections and CLEAN the surfaces....all of those grounds have paint under them, don't be shy with scraping some of the paint away and putting a little electrical grease on them.

One connection that I think GM did a crap job on was body to frame. Get under the truck and its right on the passenger side...it's a thin wide strap. Take the screw out, dremel the surface clean, then reinstall!!

If you're running at ** alt, do the Big 3 upgrade (power + grounds) with 8g and you'll be happy!!!

Lets us know how it works out for you!