Pulsating lights

**JayTA98** · 02-06-2008, 02:42 AM

Hi all! Here is the situation. I was driving yesterday on the highway and I noticed my front headlight pulsating. When I got home I checked and all my lights inside and outside are pulsating. The voltage in the 2 guages I got is normal at driving(14-14.2). When it is at idle in gear is dropto 13-13.5 and eventually goes to the yellow area. I had this problem with the voltage drop before and I changed the alternator 2 times in a row and it didn't fix it but the pulsating lights never happened before. The car has never shut off or has gave me any big problems. I haven't changed the battery cable since I got the car. I put a brand new optima battery 4 months ago. I'm pretty sure I cleaned all the electrical connections. I heard that this could be a diode in the alternator. Any suggestions? Should I'll buy a brand new alternator? Someone said something about checking an excitor wire? that fixed their voltmeter problem. I'm not so concerned with the voltmeter since it has been doing it before. But the pulsating lights is concerning me. Thanks.

**blackbird99** · 02-06-2008, 07:16 AM

i have that same problem with the pulsating lights!im thinking its the alternator

**TransAm11973** · 02-06-2008, 12:49 PM

i would definately say its the alternator, BUT.....if you have replaced your alt. twice already, then you problem is something affecting the alt. I cant tell you what that would be, but my advise is to trouble shoot that way. B/c it sounds like somethings is making your alt. go bad. Its very unlikely to have 3 bad alternators in a row.

**Spaz** · 02-06-2008, 01:06 PM

Originally Posted by JayTA98

Hi all! Here is the situation. I was driving yesterday on the highway and I noticed my front headlight pulsating. When I got home I checked and all my lights inside and outside are pulsating. The voltage in the 2 guages I got is normal at driving(14-14.2). When it is at idle in gear is dropto 13-13.5 and eventually goes to the yellow area. I had this problem with the voltage drop before and I changed the alternator 2 times in a row and it didn't fix it but the pulsating lights never happened before. The car has never shut off or has gave me any big problems. I haven't changed the battery cable since I got the car. I put a brand new optima battery 4 months ago. I'm pretty sure I cleaned all the electrical connections. I heard that this could be a diode in the alternator. Any suggestions? Should I'll buy a brand new alternator? Someone said something about checking an excitor wire? that fixed their voltmeter problem. I'm not so concerned with the voltmeter since it has been doing it before. But the pulsating lights is concerning me. Thanks.

bad ground maybe...

**JayTA98** · 02-06-2008, 04:29 PM

I did replace the alternator twice before. The 1st one was when i got the car and I was suspecting of a voltage problem. It turned out to be bad alternator. the second one I replaced it just to try to see if I had another bad alternator and it turn out to the fine when they bench tested. So really I had just replaced the alternator once. I'll check and see.

**JayTA98** · 02-08-2008, 11:18 AM

I'm happy to inform that it was the alternator. I had a bad time trying to get it exchanged because when they bench test it it was fine according to them. It was the regulator going bad. So after a few discussions and some anger they finally agree to swap it. Problem was solved once I put the new one.

**bamaz28** · 02-15-2008, 07:38 AM

MY 03 S-10 did the same thing i called the dealership they said its normal.
i bought it new and sold it with 110,000 on it, never had an alternator replaced.

**JayTA98** · 02-15-2008, 12:01 PM

To me is not normal because it wasn't doing it before. The problem is the voltage regulator starts to go bad. If you check it, the alternator is charging but mine voltage will start going up to 15.1 volts. The pulsating lights is pretty noticeable is not a lightly pulsation is it pretty bad. I had this problem in the past and it had being the alternator's regulator going bad. I just replaced the alternator and the pulsating lights are gone.

**z28punk** · 02-15-2008, 07:43 PM

My car does that too. i did an output test on it at work and it is putting out 90 amps. I asked the senior corvette tech how to fix it (worked on vettes there 35 years) and he says that he has tried to fix corvettes with this same problem and he says it almost never gets fixed. he talks to an engineer at the corvette plant regularily. im surprised that he hasnt asked him how to fix the problem.

**CJREX** · 02-16-2008, 04:50 AM

There is a TSB concerning this problem.

TSB #3170E, but I can't find anywhere I can read it without having to sign up for a service. I have been told that the dealer will print these out for you if you ask but I don't know how accurate that is..

The gist of this TSB is that there is a screw somewhere in the alternator that gets replaced.

Anyone have access to Alldata?

**z28punk** · 02-16-2008, 12:13 PM

i got access to GM's service manual online

Any vehicle may have a low voltage display (if equipped with gauges), lights that dim at stop lights, slow cranking, no start, low generator output at idle or dim lights at idle when electrical loads are heavy at idle or under slow driving or infrequent usage conditions. These characteristics may be more noticeable with customer added electrical accessories, or with a discharged battery. These are normal operating characteristics of a vehicle electrical system and no repairs should be attempted unless a proven fault has been diagnosed.

**z28punk** · 02-16-2008, 12:14 PM

Dimming lights at idle may be considered normal for two reasons:

As the engine/generator speed changes, so will the current (amperage) output of the generator. As a vehicle slows, engine/generator RPM slows, and the current (amperage) output of the generator may not be sufficient to supply the loads, the vehicle system voltage will drop and the lights will dim. Dimming of the lights is an indication that current is being pulled from the battery. If the battery is in a low state-of-charge (discharged condition), the driver will notice a more pronounced dimming than a vehicle with a fully charged battery.
When high current loads (blower, rear defogger, headlamps, cooling fan, heated seats, power seats, electric "AIR" pump, or power windows) are operating or cycled "ON", the generator's voltage regulator can delay the rise in output. This effect, usually at lower engine speeds, can take up to ten seconds to ramp up the generator output. This is done to avoid loading the engine severely. To increase current (amperage) output, additional torque is consumed by the generator. The engine computer (PCM) will ramp up engine/generator speed in small steps so engine speed variations are not noticeable to the driver.