98 xc - Lights dim for split second / Flicker?? Any ideas?

98 XC - While driving at night, I can notice the headlights and the dash
lights dim lightly and then come back to bright. I would say it is about a
5-10% decrease. Barely just enough to notice it. It is for just a brief
split second and then back to bright. Not consistent. They can blink for
about 15-30 seconds dim / bright and then stop for ten minutes.

There appears to be no engine changes, no change in idle. No warning
lights. It can happen while idle or driving 50 mph. Flat or rough road.

Does not appear to be a loose bulb because they all dim. Any ideas. I
plan to look at it today and want to get some feedback on what to look for.

Alternator going bad? How to check? I believe my wife said she noticed
this awhile ago.

Thanks

 

You say there is no change in the engine idle speed but is it the radiator
fans starting up when the air con cuts in??

My Focus does exactly the same thing, only alittle more pronounced when the
fans start.

Tim..

 

Sounds like a bad ground connection near the battery. It could also be
a bad connection on the hot line, but less likely. The other obvious
thing is a bad connection to the voltage regulator or a bad voltage
regulator. Batteries can also get bad connections internally.

I don't think it is the dimmer relay since that wouldn't affect the dash
lights. Also, I don't think it is the instrument voltage regulator
since that wouldn't affect the headlights. This problem would be easily
visible on a voltage meter.

 

That is what I am thinking also. I will look for any loose connections. I
am sure that I will notice it on a meter but is there a way to rule out a
voltage regulator vs battery and such.

 

I made sure the AC was off. It still happens.

 

Can you hear any relays clicking either on the bright to dim or the dim to
bright parts of this cycle? It almost sounds like an electric motor is
trying to start up but is having an awefully hard time (to see this effect
try closing a closed window... I only notice it on the headlights tho)

If the dimness continues for a while it could mean this motor has got itself
spinning, but is having a hard time turning... I agree with the one post to
check the cooling fans on the radiator, motors act almost like they are
shorting out when they aren't turning.

It would be a great idea to check all connections as well.

 

The best way is to take off the battery terminals and clean them. If
that doesn't fix the problem, take off other key connections to the
battery cables and voltage regulator and clean them. If that doesn't
work, get your electrical system tested. This will check out the
battery, alternator, and regulator.