Lights flicker going down the road - 99 Astro

[SatWorld]

Unlike other threads talking about flickering lights, mine only flickers while driving down the road. Of course it's unnoticable during the day. While driving at night, there is the occasional un-flash of all lights, headlights, dashboard, radio, etc. At first I thought it was something to do with the ABS since I'll get the occasional ABS light up when hitting bumps. The flickering seemed to stop, or was reduced once the ABS light lit up. But the ABS light doesn't come on anymore since having my rotors replaced. But I still get the flickering.. er un-flashing. I'm going to call it un-flashing because it's more like all the power going off for just a split second. It happens whether I hit a bump or not. It happens even on a smooth freshly paved road. There is nothing consistant about it. Sometimes it won't happen for an hour, sometimes it happens 3 times a minute. It does not happen while sitting still, engine on or off. Just while moving. I'm wondering if it's a sudden drain on the power rather than a loss of power? I know the ABS puts a big drain on the electrical system but does anything else?

I've had the alternator replaced 3 times so I doubt it's the cause (symptom or normal for 319k miles?).

[Jasen]

How many times to you think you've turned the headlights on/off the past 319K mile.



Might start looking at the switch.

[SatWorld]

Why would the light switch affect the radio display? That stays on all the time. In fact, the odometer is lit all the time, too.

[uknoLSXtro]

I once had a lights on/off flickering problem It eventually progressed to a lights off problem. Like you it only happened on the road. In my case the battery terminal was corroded and even though the bolts were tight on both terminals the battery was arcing and causing craziness with the electrical system.

My suggestion... unbolt the terminals on the battery, look for pitting/divots on the contacts. If you see pitting/divots that may be your problem. If so, replace the battery or find a way to make better contact on the contacts e.g. replace the terminals.

I hope this made sense...

[SatWorld]

I did that a couple of years ago, but I'll check them out. Time for [another] new battery anyway.

[Lumpy]

EVERYthing flickers except the engine?

That doesn't narrow it down much, but it does seem to narrow it down to NOT being the major ground cable from the battery. Some cars are wired positive cable to starter then everything else from there "back" to the fuses and accessories. Others are wired positive to the starter, 2nd big positive to the accessories. I think in your case, I'd see which I have and then look at any/all connections to the accessories. That's why it doesn't narrow it down much. But if it is everything all at once (but the engine) that suggests it's one major connection, not a dozen different, smaller connections. Fusible links, firewall pass through etc, all the usual culprits.

It it happens on bumps or vibrations, as I think you're describing, that seems like it's more likely a LOOSE connection than a shorted connection. I'd start at the fusible links and start loosening and retightening everything I could reach without too much trouble. If that solves it, great. If it doesn't, then I'd try doing the same thing but for the more difficult to reach connections.

Don't put too much faith in continuity testers or VOMs. It's probably a continuous circuit at rest. It's the bumps and vibration that's opening the loop.

Electrical ghosts are my least favorite problem.


Lump

[uknoLSXtro]

Electrical ghosts are my least favorite problem.

Agreed.

[SatWorld]

I don't think it's related to hitting bumps, because it will happen on smooth roads, but it doesn't happen on all bumps, in fact rarely on bumps. And Michigan is a great testing ground for bumps.

The engine doesn't seem to be affected by it. I looked at the log from my new OBDII scanner and it didn't show any big drop in voltage. But then again, the scanner only checks every few seconds and the loss of voltage is just a flicker, so it probably didn't catch it.

I have the one massive wire system.. alternator to starter, starter to battery. Yes, I also replaced the stater a couple years ago. This is an old, on-going problem. This isn't new. When I first noticed it years ago, I spent a couple hours in the dark, with the lights on, wiggling wires, even the big ones going to the starter. I did that after my 2nd new alternator, thinking the short or loose connection was blowing them. That's why I'm leaning to something causing a a load. It's not getting worse, so I've been living with it. You're only hearing about it now because I just joined and can ask others about it.

[Lumpy]

...That's why I'm leaning to something causing a a load...

I don't think the symptoms suggest that. I can turn on seven sealed beam off road lights while keying up a ham radio (big load) and the worst that will happen is the headlights might dim for a moment while the alternator catches up. A big load wouldn't tend to cause a flicker/blink situation. You've got at least a 100A alternator. You don't have any accessories that are drawing enough current to pull more than 100 amps.

And the only loads that happen in your van are happening when you're parked as well as when you're driving down the road, bumpy or otherwise.

Might be a connection at the positive output, rear of the alternator. Whatever it is, I really think the symptome point to SOMETHING loose, somewhere.


Lump

[uknoLSXtro]

Maybe mice, If that's the case your in trouble you'd have to OHM every wire to figure it out. A bad ground is very possible too.

[SatWorld]

I can turn on seven sealed beam off road lights while keying up a ham radio (big load) and the worst that will happen is the headlights might dim for a moment while the alternator catches up.

Exactly my symptom.

Have you ever seen what happens when you brake on ice/snow and your ABS kicks in? Major light dimming... multiple times... along with all the noise. lol I used to get the ABS light flickering and when it did, the lights dimming would be worse. That happened when hitting bumps. Once the ABS light kicked on solid, the dimming seemed to stop. I'm thinking maybe the sensor is out of wack and trying to kick the ABS in? Just for a split second?

I wonder if the scanner can monitor the ABS signals? Probably with the Pro version plus a GM enhancement, eh?

[SatWorld]

I drove for 2 hours in the dark this evening.. do you think the lights flickered even once? NOPE! I guess talking about it here fixed it. lol Or was it the new water pump? Stupid van!

[alexalexanders]

Why would the light switch affect the radio display? That stays on all the time. In fact, the odometer is lit all the time, too.

When your headlights kick on the radio and odometer go to "night mode" and become more dim. Does every thing go totally off, like if the van wasnt running?

[SatWorld]

When your headlights kick on the radio and odometer go to "night mode" and become more dim. Does every thing go totally off, like if the van wasnt running?

It's so quick, it's hard to tell. It did it a few times last night, so the problem is still there, but nearly as bad as it used to be. Could be why the alternator has lasted more than a year.

[smokinjoe]

It is bad contact in the dashboard switch for the lights. Replace that and your problem will be solve-ed.

Like alex said, the whole dash & radio dims dramaticly when the lights are turned on so the short/poor contact there is tricking you

[SatWorld]

Even when the switch is off? I monitored the voltage with the scanner for a good 100 miles today. The quick dip in voltage happens sparatically, but for a several minute period, then nothing for a long time. It does it with everything turned on (350w inverter, lights, A/C, radio and with everything turned off. During the period that it does it, switching anything big on causes a dip, A/C, elect window, lights. During the period where it's quiet, nothing causes any dips. Go figure.