Noticable electrical power drop under light load? Any ideas?

[SShockwave]

Hey Guys,

I have a 96 K1500 Z71 with the 5.7L Vortec that's all stock. A couple months ago I noticed that my voltmeter would dance drop to 11-12v when I put on the blinker. Lately it's gotten worse to where I can visually see a voltage drop in the interior lights when I press and hold one of the windows switches for example even after it's up all the way to create increased load. If I put too many accessories on the truck appears to have a minor idle stumble.

The battery is a one year old Optima Red Top, the alternator is a brand new AC Delco unit. I just put it on yesterday hoping that would fix things. While the needle swing is less, it's still there and I can see the interior lights dim when I create load on the system. It didn't do this before. All other gauges work perfectly.

Any ideas? Is this a bad battery causing the alternator to work harder to recharge it when it's running there by causing the more than normal volt drop when I create a small amount of load on the system? What else should I check. BTW, I don't have a hand held voltmeter .

 

[1993GMCSierra]

Both my '93's have done this as long as I have owned them. I wouldn't be too worried about it.

 

[jdavis8317]

i would also like to find out the answer to this as mine is doing the same and my battery is only two days old

 

[GMCTRUCKS]

It's a bad ground check battery connection or where it grounds to the frame also putting a better ground for your alternator will help as well.

 

[Tony_SS]

My volts drop only when it rains and I run the blower motor... strange indeed.

 

[Blue95]

Grounds are corroded, as stated above you need to check all of them and clean them or upgrade the wiring. Grounds are from the batt, block to frame, and alt to frame I think.

 

[JonZ71]

and do the big 3 mod.

 

[STEBS]

definatly sounds like a ground issue


the only question i have is, at night with the headlights on, do the lights pulsate? if so its a bad diode in the alt... one of my service trucks went thru 3 aftermarket altinators before we finally got 1 with no issues...hope this helps

 

[michael hurd]

Sounds like a poor ground for the alternator..... I recently had this problem, swapping in a nice powdercoated bracket, effectively insulating the alternator from the ground, which is only provided by the bracket bolted to the engine, which is in turn grounded to the battery. Alternator would not charge... I changed the alternator for a good known spare, and it still wouldn't charge... LOL.

Zero ground... I clamped a heavy set of booster cables on the alt frame to the neg terminal, charged great.

There is a hole tapped in the rear of the alternators, not used on the gas engines. ( on the diesel, there is an extra bracket bolted there ) The bolt thread is M8 x 1.25 pitch, I would procure a bolt, and put a nice heavy ground straight to the battery.