Lights pulsating

**bkdraft** · 01-07-2009, 08:20 AM

2005 Sierra Denali, 60,000 miles. Couple of days ago I noticed the lights pulsating. Its all the lights, dash, headlights, everything. It comes and goes. The alternator needle moves around a lot while this is happening, rangeing from just under 14 to nearly 15. I am guessing either battery or alternator, but not sure which. I have never seen or heard of this before. Anyone else seen this before?

**jprimrose4292** · 01-07-2009, 11:34 AM

sounds like the alternator. probably a bad regulator in it. You can take the car to just about any any parts store and they will test the electrical system on the car.

**JMoney02** · 01-07-2009, 05:45 PM

Good suggestion, also ask them to perform a load test on the Alt/Bat, they should have the tester. It has a pos/neg alligator cables on the unit and a switch and a meter. It checks what the alt/bat are doing. It will also check all accessories(load on the alt/bat, not the accessories) on these when everything is on....Jeff

**Big_Blue** · 01-07-2009, 06:58 PM

I can't see a "new" truck having connectors coming loose, but check the power connectors on the alternator and on the battery.

**chevygurl** · 01-07-2009, 09:20 PM

for the MOST part, batteries don't go bad by themselves, the alternator is usually the culprit.

I wouldn't recommend going to Advanced (at least not in my area!) to get it checked. My friend's car was acting up, and she took it there to have it tested. They told her that it was her battery that was bad, and sold her an $80 battery. I showed up and asked them to test the alternator, and they told me they could not (when I have had vehicles tested there in the past). I took her over to a starter/alternator shop, who used the same machine Advanced has and her brand new battery was already dead in a 10 min drive because the alternator wasn't working AT ALL, the engine was running off the battery alone. She may not have had to replace her battery

But that's just one store, kinda left a bad taste with me on Advanced though...

You can also check to see if your battery has water or not (it should have that kind of battery in a Denali). My 05 Trailblazer's battery rundown protection wasn't working and when I took it in the battery didn't have any water, but it was 3 years old anyway

**bkdraft** · 01-07-2009, 10:09 PM

I will get it checked, but think its going to be the voltage regulator going bad.

**Heineken** · 01-07-2009, 11:17 PM

Prolly the alt. Sounds like a bad diode

**bkdraft** · 01-13-2009, 08:09 PM

Ok, talked to a former shop foreman and he told me something to check. Turns out on the frame just under the drivers door there are two ground wires. I removed the bolts, used a wire brush on a die grinder and polished up the frame, then cleaned the wire ends real good, then bolted them back up. So far, looks like this has fixed the problem.