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Pulsing Dome Light


SM 2003
Full Member
Apr 25, 2002
Sykesville, MD
I couldn't find any threads on this and I just noticed it. I was BSing with a friend of mine showing off my AV and I turned on the dome light manually via the thumb wheel on the dash so he could see the interior. I noticed the dome light was pulsing / flickering slightly like there was a bad connection or bulb :6: . The truck was running and in gear. I put it in park, still slightly flickering and when I shut the engine off it stopped. The light is bright and steady. The voltmeter look normal and everything else looks fine. I started it up and the same thing happened when I turned the light on with the engine running. ??? Anyone got any ideas? :(
Don't know why but mine does it too. I'm going to take mine in to have the "Experts" look at it.

Don't know if its related but my clock has reset itself twice now. Usually happens at night when I start it. Something else for them to check.
Hey Rescue_1:
That's funny you mention the clock. The radio in my wifes 01 Tahoe has locked (anti-theft) all by itself about 4 times in the past year for no reason.

Please let me know the results of your trip to "expertville".

Truckman :B:
Hey Truckman,

Was this occuring at night with the headlamps and or Parking lamps on while the engine was running?

Also, Did it go away if you rev the engine ?

If so, It is most likely from the Engine Management system reducing the engine idle to a minimum for emmisions purposes. At the low idle which is around 550 rpm the alternator is not fully stable in it's output and the engine management system which does pulsate in it's monitoring is more apparent.

My Guess .....

I concur with Xrover.

I was stuck in standstill, bumper to bumper traffic yesterday on a 90 degree Texas spring day, and as the cars were not moving I decided to do some inner dash exploration. I took off the main dash bezel and was monkeying with the cargo light. I noticed that the yellow light that comes on to signify the cargo lights are activated was pulsing.
During the rare and infrequent periods where I actually moved forward, the pulsing stoppped. The electrical guage was dropping from 14 down to around 12.5 during the pulse periods. (stopped, idling in drive, foot on brake, with radio and frigid air blasting)
I attribute the pulsing to the alternator load.

Helmet, You are a trend setter. Who needs to wait for the weekend to start modding.

Heck why not start tearing things apart when your stuck in traffic. YA HOO !!
XRover said:
Helmet, You are a trend setter. Who needs to wait for the weekend to start modding.

Heck why not start tearing things apart when your stuck in traffic. ?YA HOO !!
;D ;D ;D ;D ;D ;D

An overturned diesel truck shut down the interstate for three and a half hours. I was blocked in on all sides. If I would have had my tools with me, I could have gotten some of those "projects" done. ;) Maybe even changed the oil and rotated the tires. ;D ;D

Check and see if it other bulbs are pulsing also. I was a product development engineer for a supplier to GM, and one of the products I worked on was a dimmer switch for the Olds's intrigue ( dimmed radio, hvac and all instrument panel switches). For short circuit protection, the controller used Power Transistors that had shutdown protection built into them when the transistors started to overheat (caused by either a short in the vehicle, or if the interior was extemely hot while the module was active under worse case power conditions - lights dim - it would get so hot that it would shutdown). After shutting down, it would cool off, and turn back on again. IF the vehicle was still hot, or the short was still present, it would repeat the cycle. This would cause the pulsing effect you see.
I notice this pulsing effect not with just one bulb, but with all the lights in the dash....they some time keep in beat with the base....I would attribute this to the alternator also.... :)
A thought, the 105 Amp alternator is on the weak side, at idle it really doesn't produce much beyond the current needed to charge the battery. My $.02 ;D
If it was the alternator or something along similar lines, it would be more like a dimming effect, not a full on / off sequence like he is seeing... Just another $0.2 ;)
DOME LIGHT UPDATE: I may have jumped the gun on this. I finally got to check the dome light in my wife's '01 Tahoe since the cab is almost identical. Under the same conditions, both trucks act very much alike. The Tahoe isn't as obvious, but it still pulses. :cautious:

I think XRover may have nailed it. At least it makes sense.
I wouldn't worry about it. As long as it stops pulsating with the slightest increase in RPM your situation is normal I'm sure.

Well I have been paying more attention to it, no it doesn't stop with an increase in RPM's. Doesn't change speed (flashrate) either.

My clock hasn't acted funny lately but the dome light, actually see it on dash lights too, still pulses. I had originally thought it was the dimmer switch, but then I noticed the dome light too.

I haven't taken it in yet, I guess it can wait till I reach the 5000 mile mark.

BTW when I first start my AV the red battery indicator flashes a few times, is it related or normal? I realize the battery is drawn down while cranking but I didn't think it should stay on for more than a second or two. It doesn't stay on long maybe three seconds, or like three flashes. The guage stays steady at 14 volts.

Hey Rescue_1:

I also notice the red battery light sometimes stays on a couple of seconds when I start up. It doesn't flash, but take a 2-3 seconds to go out. I don't see that with my '01Tahoe and they are basically the same vehicles. I may take it by the dealership. Unfortuantely, I've got a good relationship with my saleman, but the shop sucks and if you take your truck to a dealer other than the one you bought it from, they don't even want to talk to ya'. I wish I could find a good saleman and decent shop to go with it.

Truckman :B:
Rescue_1 said:
Hey G-man, how about I swap it out with that 200 Amp unit...

I am going to attempt to shoehorn a Powermaster 200 in mine. The Whipple forced me to move the alternator from the 2 o'clock position to the 11 o'clock location, it's going to be tight.

I would have preferred one of the others, but no way to fit it.
Hey rescue, I thought you wanted flashing lights ?>:D

As far as the red Battery warning on when starting the vehicle, that is normal for a second or two.

If you rotate the dimmer switch, do the dash lights get brighter and dimmer SMOOTHLY or do they get jittery ?

Maybe there were a bad batch of dimmer switches or alternators ????
As far as I remember, the dash lights are smooth. Of course its daytime so I'll have to check it out later tonight...

BTW I have the strobes in, now for the rest of them...